Your name.
Ok, got some sats from nostr:nprofile1qqsyvy7nyz4gsqne9fdz7v6f5gs8uvhkw85vqsq9srwuxrk6dlwlv2spzpmhxue69uhkummnw3ezuamfdejsz9nhwden5te0wfjkccte9ehx7um5wghxyctwvsq32amnwvaz7tm9v3jkutnwdaehgu3wd3skueqs99vq0 so:
First Correct answer wins 1111 sats.
What belongs to you but is used by everyone you meet?
Your name.