The trouble with common names is they sometimes refer to entirely different genera. Here's a photo of a club moss Selaginella kraussiana brownii which is also known as Irish moss. If what you have is this, it is not a flowering plant as someone suggested in an earlier post, but a club moss and is excellent for terrariums. Yours is a much better speciemen than mine, as well as a better photo, but superficially, it looks pretty much the same to me.
The other "Irish moss" I know of is Helxine soleirolii, also called "baby's tears," and is a flowering plant related to the pileas, but it is totally different, with tiny rounded leaves. (I have some of this too, and it's also a great terrarium plant.)