What is the difference between daily retention and monthly retention?

I know the obvious answer is one refers to retention for the entire month and one is for the day. While I understand monthly retention pretty well, I'm trying to wrap my head around what daily retention would look like. For context, I work at a dealership and monthly retention is basically my whole job as it's my job to call people who haven't been in for service in a while and get them back in. But our DAILY retention is way down and I don't know what that means and I'm trying to figure out if it's my fault or not lol