EDIT Earliest use Equality. In printed books before the modern equal sign, equality was usually expressed with a word, such as aequales, aequantur, esgale, faciunt, ghelijck, or gleich, and sometimes by the abbreviated form aeq (Cajori vol. 1, page 297).

The equal symbol (=) was first used by Robert Recorde (c. 1510-1558) in 1557 in The Whetstone of Witte. He wrote, "I will sette as I doe often in woorke use, a paire of parralles, or Gemowe lines of one lengthe, thus : ==, bicause noe 2, thynges, can be moare equalle." Recorde used an elongated form of the present symbol. He proposed no other algebraic symbol (Cajori vol. 1, page 306).

The equal symbol did not appear in print again until 1618, when it appeared in an anonymous Appendix, very probably due to Oughtred, printed in Edward Wright's English translation of Napier's Descriptio. It reappeared 1631, when it was used by Thomas Harriot and William Oughtred (Cajori vol. 1, page 298).

Cajori states (vol. 1, page 126):
A manuscript, kept in the Library of the University of Bologna, contains data regarding the sign of equality (=). These data have been communicated to me by Professor E. Bortolotti and tend to show that (=) as a sign of equality was developed at Bologna independently of Robert Recorde and perhaps earlier.
Cajori elsewhere writes that the manuscript was probably written between 1550 and 1568.

Source: A History of Mathematical Notations, Cajori, vol. 1

 84.176.184.170  84.176.185.80 

EDIT Mathematics The amount to the left of the character is equal to the amount to the right of the character.

 jsw 

EDIT Relational operator The character is one of five relational operators in mathematics. They have the function of specifying a comparison between two values. The others are:

U+003C < Less-than Sign
U+003E > Greater-than Sign
U+2264 ≤ Less-than Or Equal To
U+2265 ≥ Greater-than Or Equal To

 jsw