Aida is the most popular needlework fabric for cross stitch. It is woven with the threads grouped into bundles to form a square pattern on the fabric. There are small holes on each corner of these squares to stitch through. The smaller the Aida count, the easier it is to see the holes as the holes are bigger. 14 count is the most popular count and great for beginners.
Evenweave (e.g., belfast, cashel) needlework fabric has threads woven singly rather than blocks. Cross stitch patterns that can be stitched on aida can also be stitched on evenweave. Your pattern may say ‘over two’ (that is, stitch over 2 threads); or ‘2 by 2’, or ‘2 over 2’ (that is, stitch 2 strands of floss over 2 fabric threads). This is common but working over one with one thread can be done when very fine detail is required.