I divide 1RM into 2 categories:
Personal Best (PB): This is the most an individual will lift with proper form and that is repeatable. While you wont be able to hit it all the time, it's a weight you should be able to lift at least once a week if you tried. Could also be seen as "the best you can do".
Personal Record (PR): This is the most you ever lifted on a movement. Sometimes it is done with some form breakdown and it is also sometimes a freak occurrence (happened to be one of those great days). Because of these two factors, a PR is not as repeatable as a PB... it's something that you hit once but might have to wait a while to be able to hit again.
When I design programs I prefer to use the personal best as a measure. The PR is mostly for bragging rights.