British Invasion refers to the act of popularization of British music and bands in the US. It started in the 1960s, particularly 1964, which is the first time the Beatles visited the US. They arrived in the US on 7th of February, two days later they would go on to play one of the greatest live TV shows of all time.
They were supposed to play to an audience of 728 people (which was the capacity of the ed Sullivan theatre) after receiving over 50000 ticket requests.
On 9th February at 8 pm 73 million people tuned into their TV sets to watch the Beatles live. This holds a very significant place both in the British invasion and the start of Beatlemania in the US. This kind of number was never seen before on live television. They would go on playing two more shows, one live and one taped later the same month.
This acted as a ticket for other British bands to the US. Other popular bands like the rolling stones and the kinks would soon follow.