Typical entries from the conntrack database might look something like:

tcp      6 254365 ESTABLISHED src= dst= sport=13449 dport=25 packets=5 bytes=339 src= dst= sport=25 dport=13449 packets=6 bytes=572 [ASSURED] mark=0 secmark=0 use=1
Which all makes sense except for the very last bit, use=1. I've actually been working with Linux for several years now, and am just realizing I don't know what that part refers to.

Can anybody shed some light on this?