What is the Northern Ireland backstop exactly?

Ireland has enjoyed an open border between the North (which is under UK rule) and the South which is a separate country since about 1998. Without the need or want for an official manned/guarded border.

The reason for this is all part of an agreement between both countries set up in the late 90's that also saw an end to terrorist activity from factions in the North opposed to rule under the UK.
(See: The Good Friday Agreement)

The E:U wants a border between the two countries once the UK leaves the E:U.
Reason being that the South is a member of the E:U and will continue to enjoy trade benefits. But the North will leave along with the UK and the E:U wants to prevent the North from being able to enjoy the same benefits the South has. Specifically, freedom of movement and lack of import tariff for goods from the E:U.

With me so far ?

The E:U's 'worry' is that there'll be some sort of smuggling operation from the South to the North. And the North will obtain goods from the E:U without having paid the import tariff.

The proposal known as 'The Backstop' would see the North enjoying (effectively) membership of the same trade deal that the South has. Whilst negating the need for walls; physical borders; customs checkpoints etc.

Point being that neither the UK nor the E:U tries to separate two countries that have seen more than their fair share of political/religious segregation throughout their history.

The 'Backstop' is a UK proposal that the E:U is broadly in favour of but 'May's deal' is a bit vague as to how it would operate.
I suspect because it needs clarification and agreement from the other E:U member states before being confirmed.

It was something that Theresa May agreed with the EU about a year ago and is trying to bail out of.

Basically, it means as a default and non-negotiable option that Northern Ireland stays in the single market and the customs union.

All Northern Irish and Southern Irish parties determined to keep this in place because they trade with each other a lot and because many many businesses on both sides of the border are mutually dependent. As long as this remains in place you can't have a hard-Brexit and total break.

The DUP (which has been propping up May's Government) don't like the Southern Irish but they don't wanna tank their own economy. They have broken with May because her current 'compromise deal' between hard and soft Brexit leaves open the possibility for customs checks between Northern Ireland and the rest of the UK. The DUP are hardcore unionists and are vehemently against any deal which would take Northern Ireland closer to the Irish Republic than to Britain.

I hope that explains it a bit but I know its really complicated and messy.

It's meant to prevent the introduction of border controls between Northern Ireland and the Republic of Ireland. No-one really wants these as they're a key part of the peace process. The DUP interpretation of the backstop measures is that they create a different set of laws in Northern Ireland to the rest of Great Britain and therefore weaken the union they want to preserve. In reality, Northern Ireland already has a separate legal system and differs to rest of UK in several areas.

the people were lied to well kinda obvious lies but they worked on the stupid people that voted for a brexit...

if the brits have any sanity they cancel this madness