At some indefinite or unspecified time.

कभी

English Usage: I will call you sometime later.

Hindi Usage: मैं तुम्हें कभी बाद में फोन करूंगा।

An unspecified time in the future or past.

कभी

English Usage: We should meet sometime next week.

Hindi Usage: हमें अगले हफ्ते कभी मिलना चाहिए।