WebOps-related mailing lists have always had a problem with this vague term, and I suspect that commercial vendors exploit this confusion.
Wikipedia gives a pretty vague definition:
“…is the process of testing or tracking (monitoring) how end-users interact with a website or web application.”
People use the term to describe lots of things that pertain to the web:
I wish I knew of a better way to disambiguate the term in an easy way. I suspect that the tools listed above will always use the word ‘monitoring’ in their descriptions. Sigh.
Relatedly, I have the opinion that the three different functions listed above should be performed by different pieces. I’ve yet to see any tool that sucessfully combines health-check/alerting with resource trend/graphing, for example. I don’t have much experience with GroundWork or Zabbix, maybe folks who do can argue with me on that point.