What’s the meaning of this signal?

Explanation: The green light indicates that regular traffic can continue if it is safe to do so, while the white line tells trams to stop. Even if there are no trams where you normally drive, you should be familiar with signals applying to trams, as they're being introduced in more and more places.

Category: Road and traffic signs (2021)

References: The Official DVSA Guide to Driving: Section 6, Highway Code: Page 102, Know Your Traffic Signs: Page 31