OTE is an abbreviation seen in situations vacant advertisements, usually in a sales or pre-sales capacity. The advert will read something like:
Salesman Wanted, Birmingham Area, Basic: 15k OTE: 40k
In this context, OTE stands for On-Target Earnings. The job will pay a basic rate of 15k, with the remainder made up from bonuses and/or commission. The 40k value is an estimate of possible earnings including base and bonuses if 100% of sales commitments are met.
It is possible that actual earnings will be lower or higher, depending on performance. The basic rate is usually guaranteed monthly, and the bonuses may be bi-monthly, quarterly or on any other schedule.