Rogue talent · row 6 of Combat, from level 35 (30 with Talented 5/5) · Physical

Aggression

Increases the damage of your Sinister Strike, Backstab, and Eviscerate abilities by 2/4/6%.

Game files · build 1.60.1.70291Read straight from the WoW Forever beta client.

Compared with Classic

Classic tooltip

Increases the damage of your Sinister Strike and Eviscerate abilities by 2%.

What Blizzard said about Aggression, each line checked against the files.

Matches the files
Aggression: Now also increases Backstab damage. We wanted the Combat specialization to support a Backstab-oriented build as well as a Sinister Strike-oriented build. So, this and several other talents gained more Backstab support.
The files Aggression (18427) lists Sinister Strike, Backstab and Eviscerate at 2/4/6%; Classic's tooltip had no Backstab.
Aggression Class deep dives: Rogue and Warlock

69876 Sep 16First beta build we archived. No changes in the client files since.