What are dominant 7th's and is it the same as a major 7th chord?

E7♯9 guitar chord chart
E7♯9, known by guitar players as the "Hendrix Chord" in guitar chord chart format. By Drew Von Buseck (© 2009 Drew Von Buseck) [ GFDL or CC BY-SA 4.0-3.0-2.5-2.0-1.0], via Wikimedia Commons

A dominant 7th uses the symbol of a note name + 7. For example C7, D7, E7, etc. It is different from the symbol used for a major 7th which is maj7. A dominant 7th is not the same as a major 7th chord. But, to form a dominant 7th you must know how to form a major 7th chord first because these two types of chords are related.

A major 7th chord is formed by playing the root (1st) + 3rd + 5th + 7th notes of a major scale.

A dominant 7th is formed by simply lowering the 7th note a half step.

As an example, Cmaj7 = C - E - G - B (7th note). Lower the 7th note a half step, from B to Bb, thus Dominant 7th = C - E - G - Bb.

Here are the dominant 7th chords in every key:
C7 = C - E - G - Bb
D7 = D - F# - A - C
E7 = E - G# - B - D
F7 = F - A - C - Eb
G7 = G - B - D - F
A7 = A - C# - E - G
B7 = B - D# - F# - A
C#7 = C# - E# (F) - G# - B
Db7 = Db - F - Ab - B
Eb7 = Eb - G - Bb - Db
F#7 = F# - A# - C# - E
Gb7 = Gb - Bb - Db - E
Ab7 = Ab - C - Eb - Gb
Bb7 = Bb - D - F - Ab