This is the 12077th most frequent Polish word.
liści
"Liści" means "leaves" (plural form) in English.
Here, 'liści' is used to refer to 'leaves' in the locative case because it follows the preposition 'na' combined with a statement of location.
Na drzewie jest dużo zielonych liści.
There are many green leaves on the tree.
In this sentence, 'liście' is in the accusative case as it is the direct object of the action 'zbieram' (I am collecting).
Zbieram kolorowe liście z ziemi.
I am collecting colorful leaves from the ground.
Here, 'liści' is in the genitive case, which is dictated by the noun 'zapach' (smell), often requiring the complementary noun to take this case.