U stands for University
It all started in France in 1972 when some universities opened their doors to enable retired people the opportunity to continue learning. In 1982 the UK u3a movement started and it was decided not to use universities, preferring local amenities and local knowledge, but still enabling continued learning.
3a stands for 3rd. age.
1st. age. Childhood, school years and further education. Making friends and socialising.
2nd. age. Working, marriage and family. Still learning and making friends and socialising.
3rd. age. Retirement/semi-retirement. Still wanting to make new friends, socialise and learn new things educational, cultural and/or recreational, or return to previous pastimes.