I live and go to school in the uk and for gcse biology one of the topics is evolution. Theres always a question that comes up in the exams which is basically "what was Darwin's theory of natural selection". The answer they were looking for was along the lines of:
"A random mutation occurs in a species that alters the dna of the organism with that mutation. If this mutation is beneficial to the species them the organism is able to survive and pass on its beneficial mutation to their offspring through sexual reproduction. Over time the organisms without this mutation die out leaving only the ones with the mutation left."
I always enjoyed seeing that question in an exam because it was an easy 4 marks. It was also the definition I gave to my mum when she did a dub and confused evolution with abiogenesis.
I'm not 100% if this is right though because they have a habit of leaving out all the details and stuff out of gcse level science