Simplify the following text for a Grade 8 native English-speaking person.
Original: As a separate genre , it appears to have no specific form , although most of the divertimenti of the second half of the 18th century go either back to a dance suite approach ( derived from the ` ballet ' type of theatrical divertimento ) , or take the form of other chamber music genres of their century ( as a continuation of the merely instrumental theatrical divertimento ) . There are many other terms which describe music similar to the divertimento , including serenade , cassation , notturno , Nachtmusik ; after about 1780 , the divertimento was the term most commonly applied to this light , `` after-dinner '' and often outdoor music .
Simplified: The divertimento became popular in the 18th century .