What does this "en" represent? Merci

[Une]

Nous mangeons avec celle-ci assez régulièrement, mais en ce qui concerne les autres, nous avons été très négligents.

[Frank]

Hello Une,

This "en" doesn't refer to anything in particular.

It's part of the expression en ce qui concerne, which means regarding or according to

[Frank]

... or as far as someone is concerned, which is even closer :)