i believe the gift tax applies once you get above $14,000 in value in any given tax year.
Person A can give persons C and D $14K each and that all falls under the annual exemption. Persons A and B can together give person C $28K and person D $28K and still be within the exemption (2 spouses giving to 2 kids is a common example).
Source: https://www.irs.gov/businesses/small-businesses-self-employe...
In the US, any gifts over $5.49 million over the course of your lifetime is taxed.
Any gift over $14k in a single year needs to be disclosed to the IRS, but it's not taxed. They're just keeping track of it in case you hit the $5.49 million lifetime cap, and they reduce the amount of your estate tax exemption by that amount.
It's all set up to stop people from avoiding the estate tax by gifting a lot of their wealth while alive.