"Rags" is the short-form or colloquialism of "Ragtime Songs". They are one and the same.
My understanding of Ragtime as it applies to fingerstyle acoustic guitar (and please, anyone correct me if I'm wrong) is the concept of keeping a strong alternating bass going with the thumb, while playing chords and melody lines with the other fingers. The thumb simulates what the left hand would be doing on the piano and the other fingers simulate what the right hand would be doing on a piano.
Generally this style is characteristic for Ragtime pieces however there are many many folk and country blues songs that follow this format as well, which are not considered Rags.