Break clause and what is it?

How does a break clause work and what is it? Mine says it can be activated after 4 months. Is this if I want to end a tenancy early and exit without paying the remainder of the tenancy?

Usually yes, but it depends on the wording. What exactly does yours say?

12.6. The Initial Term of this tenancy agreement may be terminated by either party giving the other at least two
months’ notice in writing, such notice not to expire until at least 6 months after the start of the Term. A noticeserved by the Landlord under section 21 of the Housing Act 1988 shall be sufficient notice under this clause.
The Tenant is obliged to pay rent up to and including the termination date, so if the tenancy is terminated on a
date which is not the last day of a rental period, the rent due for any incomplete rental periods will be apportioned accordingly.

this is the paragraph with the clause. And it says on my openrent dashboard it can be activated after 4 months and I have to give 2 months notice.

Yes, it sounds as though you can do that and that you don’t need to worry about the notice expiring at the end of a tenancy period either, just as long as its expiry is at least 6 months after the tenancy began.

So by the looks of it I can leave on the 6 month point and not be liable for the remaining 18 months of rent as it is a fixed term tenancy

It looks that way, yes.

As said above providing you give two months notice that’s the key, but the best way , if you are planning to leave is to talk in principle to your agent or landlord. If they confirm it you know your status.