German term (edited): UK (Unterkante) Bodenplatte

UK – Unterkante
http://www.bauherrentipp.de/abkuerzungen.htm

UK Unterkante
UKA Unterkante abgehängte Decke
UKD Unterkante Decke
UKR Unterkante Rohkonstruktion
https://www.code-knacker.de/bauplanzeichen.htm

Unterkante f / 1. bottom edge, lower border, 2. (Verk) lower flange (Stahlbau)
Bodenplatte f / floor slab, floor slab (Fundament); bedplate soffit slab, base plate (Anlagen)
(Gelbrich, Fachwörterbuch Architektur und Bauwesen)

Bo·den·plat·te SUBST f BAU
Bodenplatte floor slab
https://de.pons.com/übersetzung/deutsch-englisch/Bodenplatte

Die Gründungsfläche entspricht dem Umriss der Bodenplatte bzw. den Außenkanten der Streifenfundamente, gelegentlich wird auch von Gründungsebene gesprochen.
:
Das Fundament kann als durchgehende Bodenplatte, Streifenfundament oder als Punktfundament ausgeführt werden.
https://de.wikipedia.org/wiki/Gründung_(Bauwesen)

There is also a concrete slab floor.
https://en.wikipedia.org/wiki/Foundation_(engineering)

A concrete slab is a common structural element of modern buildings, consisting of a flat, horizontal surface made of cast concrete. Steel-reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ceilings, while thinner mud slabs may be used for exterior paving (see below).
https://en.wikipedia.org/wiki/Concrete_slab

Dabei wurden 12 horizontale DYWIDAG-Litzenspannglieder in der Bodenplatte, 178 Litzenspannglieder in der Außenwand sowie 18 Spannglieder im Ringbalken installiert.
Die Bodenplatte wurde mit einer Ringvorspannung versehen, die abschnittsweise in 6 um 60° versetzten Lisenen verankert wurde.
www.dywidag-systems.at
12 horizontal DYWIDAG Strand Tendons were installed in the floor slab, 178 tendons were installed in the exterior wall and 18 tendons were used in the ring beam.
The floor slab was circumferentially post-tensioned with tendons anchored in 6 buttresses rotated by 60 degrees.
www.dywidag-systems.at

Dieser visuelle Eindruck wird noch dadurch intensiviert, dass Dach und Bodenplatte nach Osten, Süden und Westen weit auskragen.
architektur.mapolismagazin.com
Together, they seem like a ring binder that files the rest of the building.
This visual impression is even intensified by the fact that roof and floor slab cantilever to the east, south and west.
architektur.mapolismagazin.com
https://de.pons.com/übersetzung/deutsch-englisch/Bodenplatte

"foor slab" "bottom edge" 7 Ergebnisse (0,47 Sekunden)
"foor slab" "lower border" Ungefähr 851 Ergebnisse (0,33 Sekunden)
"bottom edge" "floor slab" Ungefähr 352.000 Ergebnisse (0,54 Sekunden)

The crane operator should lift the panel without dragging the floor slab along the slab or striking any previously erected panels.
:
After the panels are erected, the remaining steps include:
1. Making the required (if any) connections between panels.
2. Casting the pour-back strip between the panels and the floor slab by backfilling and placing concrete.
http://tilt-up.org/tilt-uptoday/wp-content/uploads/2011/11/C...

Exterior perimeter insulation consists of rigid foam insulation applied to the vertical face of the exterior edge of a floor slab. The foam insulation normally extends from just below the bottom edge of the exterior wall cladding to the bottom edge of the wall footing.
https://www.buildmagazine.org.nz/index.php/articles/show/edg...

4. A precast concrete building unit for mounting on a floor slab, the building unit comprising at least two upright load-bearing exterior walls, each exterior wall having a respective bottom edge, means for joining the exterior walls to the floor slab, and an interior wall cast integrally with at least one of the exterior walls, the interior wall having a bottom edge which is spaced above the bottom edge of each exterior wall a sufficient distance such that the interior wall does not transmit a load to the floor slab when the exterior walls are joined with the floor slab.
https://patents.google.com/patent/US3898776A/en

Additional insulation for comfort and energy efficiency can be achieved by providing:(a) insulation to edge of floor slab,
:
The minimum thickness of the floor slab shall be 100 mm – see Figure 3.1.1
:
(a) bottom chords of trusses or bottom edge of rafters
https://www.building.govt.nz/assets/Uploads/building-code-co...

To resist lateral pressure, the wall acts like a slab, with lateral supports provided along bottom edge (by basement lower border) and top edge (by first floor of house, if available and effective).
https://www.structural101.com/Cracked-Foundation-Wall.html

More particularly, the present invention relates generally to debris barriers which are installed to prevent debris and other objects from falling off the floor slab of a structure under construction.
:
The finished netting 30 has an upper border 32 and a parallel lower border 34 as well as longitudinally spaced parallel side borders 36 and 38 for each netting section. The lower border 34 may be a single ply edge of netting or a dual ply netting band.
https://patents.google.com/patent/US4875549

As the result, in the end of all framework unit beams erection and tensioning of the steel (stage 6), the cross section of the unit beam of the1-st floor is almost centrally pressed with a small difference in the tension at the upper and lower border at the bay center (1.98–2.03 MPa)
:
Applied further (stage 7) erection loads (weight of unit floor slab, weight of newly laid cast-in-place concrete etc.) lead to new change of strain distribution in the frame construction elements.
https://engstroy.spbstu.ru/userfiles/files/2017/6(74)/14.pdf

P.S. Underfloor heating Basement heated? The dew point is already in the floor slab (at the upper edge), an increase in temperature on the floor surface will move the point toward the basement, which, in the presence of cold moist air and lack of ventilation, is fraught with condensation directly on the lower border of the floor slab, where the slab reinforcement belt is located.
https://infocom-m.ru/en/poly/what-to-do-floor-on-lags-or-scr...