What’s the meaning of this signal?

Explanation: The white light shows that trams must stop. The green light shows that other vehicles can go if the way is clear. Trams are being introduced into more cities, so you're likely to come across them and you should learn which signs apply to them.

Category: Road and traffic signs (Motorcycle Theory 2021)

References: The Official DVSA Guide to Riding: Section 7, Highway Code: Page 102, Know Your Traffic Signs: Page 31