See the below table for all severity levels and a short description.
This table is borrowed from the Syslog Wikipedia page...
|0||Emergency||emerg||System is unusable||This level should not be used by applications.|
|1||Alert||alert||Should be corrected immediately||Loss of the primary ISP connection.|
|2||Critical||crit||Critical conditions||A failure in the system's primary application.|
|3||Error||err||Error conditions||An application has exceeded its file storage limit and attempts to write are failing.|
|4||Warning||warning||May indicate that an error will occur if action is not taken.||A non-root file system has only 2GB remaining.|
|5||Notice||notice||Events that are unusual, but not error conditions.|
|6||Informational||info||Normal operational messages that require no action.||An application has started, paused or ended successfully.|
|7||Debug||debug||Information useful to developers for debugging the application.|
To tone this down a bit you can change the level at which ESX sends logs.
For ESX 3.5/4.1 see the following link...
For ESX 5.1 +
Using vSphere click on a host to manage then choose the configuration tab of the host
Under Software | Advanced Settings | Config | HostAgent | log
Decrease the config.HostAgent.log.level to 'panic', 'error', 'warning or 'info' rather than 'verbose.