Tad is a variation (English and Irish) of the name Tadhg (Gaelic, Irish, and Scottish).
Tad is also a shortening (English, Irish, Latin, and Welsh) of the name Thaddeus (English).
See also the related form, Taron.
Tad is uncommon as a baby name for boys. At the height of its usage in 1966, 0.015% of baby boys were named Tad. It ranked at #473 then. The baby name has since substantially dropped in popularity, and is currently of very modest use. In 2018, within the group of boy names directly related to Tad, Thaddeus was the most popular.
† Pronunciation for Tad: T as in "tee (T.IY)" ; AY as in "side (S.AY.D)" ; G as in "grin (G.R.IH.N)"