These Neolithic monuments are usually a large mound of earth with a stone passage extending into the middle of the mound to a central chamber where there might be side-chambers. The central chamber was often found to have contained the ashes of human remains. Sometimes they’re called a tumulus.
I’ve seen them called barrows, but usually a barrow has no passage, are just a mound with cremated remains and grave goods inside. I think.
Here is a plan of the passage and central chamber in Newgrange, one of the largest passage tombs I’ve seen.
(This picture is not entirely accurate. Newgrange is designed so that you climb slightly uphill as you follow the passage, such that the central chamber is aligned with the roof box, not the entrance. That means the sunlight on the winter solstice comes into the chamber via the roofbox, not the doorway. As far as I remember, Newgrange is the only passage tomb designed this way. For more info about Newgrange, click here.)
When the mound is covered with stones rather than earth, it would be called a cairn.
Sometimes there may be a large open area in front of the entrance enclosed by stone walls. That is called a court cairn.
There are also gallery graves and wedge-shaped gallery graves, where there’s no passage.