Simplify the following text for a Grade 9 native English-speaking person.
Original: The rainbow flag , sometimes called ` the freedom flag ' , was popularized as a symbol of lesbian , gay , bisexual and transgender ( LGBT ) pride and diversity by San Francisco artist Gilbert Baker in 1978 .
Simplified: Since 1978 the rainbow flag is also the symbol of the LGBT ( lesbian , gay , bisexual , and transgender ) community . It is also called the ` Pride Flag . '