Although both Joe and Sarah are registered as users on their local UNIX system, they belong to different departments; Joe is a postgrad student in artificial intelligence while Sarah is Head of the Math Department. Their respective home directories might be:
/(root) | | ---------------------- | | /tmp /usr | | ---------------- ... ---- | | | /ai /biol /math | | ---------- --------------- | | /joe /staff | ------------------ | /sarah
The full pathname to Joe's home directory is /usr/ai/joe - that to Sarah's is /usr/math/staff/sarah.