Simplify the following text for a Grade 12 native English-speaking person.
Original: Space rock is a subgenre of rock music ; the term originally referred to a group of early , mostly British , 1970s progressive and psychedelic rock bands such as Hawkwind and Pink Floyd , characterised by slow , lengthy instrumental passages dominated by synthesizers , experimental guitar work and science fiction lyrical themes , though it was later repurposed to refer to a series of late 1980s British alternative rock bands that drew from earlier influences to create a more melodic but still ambient form of pop music .
Simplified: The term originally referred to a group of early mostly British 1970s progressive rock and psychedelic bands such as Hawkwind and Pink Floyd . The music is characterised by slow , lengthy instrumental passages dominated by synthesisers , experimental guitar work and science fiction lyrical themes .