What the hell is the Irish backstop?

UNITED KINGDOM — An integral part of Brexit negotiations concerns the border between Northern Ireland and the Republic of Ireland.
According to the BBC, last month, E.U. leaders approved a deal with the U.K. that includes an agreement on the Irish border, with both sides looking to avoid reintroducing border posts between the two areas.
According to the Washington Post, the backstop is an insurance policy that would keep Britain in the E.U. customs union if no other agreement can be found to keep an open border between Northern Ireland and Ireland.
Because the U.K. and Ireland are currently both part of the E.U. single market and customs union, goods do not need to be inspected for customs and standards, so products and services can be traded on Ireland with few restrictions.
However, after Brexit, Northern Ireland and the Republic could be in different customs and regulatory systems, which could mean hold ups for goods being checked at the border.
The problem now is that both the U.K. and the E.U. have different opinions on what the backstop should contain.
The E.U. had originally proposed that Northern Ireland stay in the EU customs union, large parts of the single market and the E.U. VAT system.
Britain on the other hand, is against having a separate status for Northern Ireland because it feels it would damage the union as a whole.
If the two sides cannot come to a deal on the backstop, it could mean a no-deal Brexit. This in turn could mean there would be some type of hard border with heavy checks in place between Northern Ireland and the Republic.