'Days Lost to Limit' is a column in the Time Off History report in Web TimeSheet 8.x versions which indicates any accruals that are lost because of Time Off balance reaching the maximum allowed limits. "The amount of Time Off Accruals lost" during this process are what Days Lost to Limit is.
Following example explains the same:
First of every month 1.25 days are accrued for this user. 40 days is the maximum balance that this user can store at any point of time as seen in the report. When the user reaches this 40 days of Time Off balance, which is, As of March 1st 2011, it is seen that 0.50 days of accrual time was lost because the total became from 39.25 days to 40 days (Accrual of 0.75 days). Therefore this remaining accrual of 0.50 was lost for the month of March 2011. If the user does not continue to take the time off, the balance remains at 40 days and hence loosing the full accruals of 1.25 days every month going forward, which is what the "Days Lost to Limit" indicates in the report.