This is the 2176th most frequent Dutch word.
lek
A "lek" in Dutch is a "leak" in English.
Here, 'lek' is used as an adjective to describe the bicycle tire being deflated and leaking air.
De band van mijn fiets is lek.
The tire of my bicycle is flat.
In this sentence, 'lek' serves as a noun referring to a hole or crack through which water enters.
Er zit een lek in het dak.
There's a leak in the roof.
Here, 'lek' is again a noun, but it specifically refers to the source of leaking water that was repaired by the plumber.