My offer letter says -- BASIC: £25,000 - £35,000, OTE; £35,000 - £45,000 open ended /achievable. What is the meaning of this
"On Target Earnings" The salary you get when you reach your targets (as defined by the company).
"BASIC: £25,000 - £35,000, OTE; £35,000 - £45,000 open ended /achievable"
That's a figure I'd expect to see in a job advertisement, not an offer letter. I'd expect a solid 'basic' number, not a range - otherwise, who decides where in that scale you fall? That should have been sorted in interviews/negotiations.
I'd expect to see something like 'Basic: £25,000, OTE; £35,000 - £45,000 open ended /achievable"
So; you're guaranteed a £25,000 salary (initially, at least). If you make the number of sales that they expect ('On Target Earnings'), you'll pick up around another £10,000 - £20,000 in commission (this sounds like a sales position). 'open ended / achievable' means that there is no limit on your commission, so if you make enough sales, you can get into six figures - or at least over £50,000. They believe that a decent sales person can achieve this (of course, they would say that, wouldn't they).
It's worth bearing in mind that if you aren't hitting your targets (and picking up the bonuses), you won't be getting the 'Basic' part of your salary for very long; there's no room for underachievers in sales.
More importantly.. Terms like 'OTE' are very common in Sales. If this is a sales job, and you didn't grasp 'OTE', then I'd guess you don't have much experience. Hit all the training you can get your hands on. It's a cutthroat industry; the best people do very well, and failures fall by the wayside.