This is the 8463rd most frequent Russian word.
нашу
"Our" (feminine singular, accusative case).
In this sentence, "нашу" (our) is used as an accusative singular feminine pronoun referring to the cat, indicating possession.
Мы нашли нашу кошку в саду.
We found our cat in the garden.
Here, "нашей" (our) is used in an instrumental singular feminine form to describe ownership of the group being helped.
Она помогает нашей группе с проектом.
She is helping our group with the project.
In this sentence, "нашем" (our) is used in a prepositional singular masculine form, denoting possession of the plan being referred to.