Kinds of grass
If you have a sunny or part sun lawn, the grass is probably tall fescue, which is the best type of turf for Maryland. It is highly drought tolerant and pest resistant. Though you may have a little bluegrass, it usually dies out over time.
If you have deep shade, the grass is probably a fine fescue.
Please read our online publication for reseeding in established lawns: http://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/HG102%20La...
We also have many other publications about how to grow successful turf in our (homepage) Library under Publications.