This is the 2658th most frequent Polish word.
biegach
"Biegach" is the plural form of "bieg," meaning "gears" (as in a vehicle) or "runs" (as in movement, e.g., races) in English, depending on context.
Here, 'biegach' is in the plural locative case, referring to events centered around running, typically as organized races on streets.
Lubię uczestniczyć w biegach ulicznych.
I like to participate in street runs.
In this sentence, 'biegach' is again in the plural locative case, referring to specific types of running competitions, emphasizing the terrain.
Podczas zawodów biegach terenowych widziałem wielu utalentowanych sportowców.
During cross-country running competitions, I saw many talented athletes.
Here, 'biegach' is still in the plural locative case, but it refers to gear settings on a bicycle rather than running events.