This is the 14722nd most frequent Russian word.
пехотного
"Of infantry" or "infantry's."
Here, 'пехотного' functions as an adjective, describing the type of regiment—'infantry regiment'.
Солдаты маршировали в составе пехотного полка.
The soldiers were marching as part of the infantry regiment.
In this sentence, 'пехотного' is used as an adjective modifying 'battalion', specifying that the battalion is part of the infantry.
Командир пехотного батальона получил медаль за отвагу.
The commander of the infantry battalion received a medal for bravery.
Here, 'пехотного' serves as an adjective to detail the nature of the unit—an infantry unit.