A walk was a type of excursion done for pleasure or exercise.
In 2266, aboard the USS Enterprise, Eve McHuron claimed to Captain James T. Kirk that she had been on a walk when she became troubled by the behavior of the male crewmembers who she thought were looking at her and following her with their eyes. Escaping the unwanted attention, she ran into the captain's quarters. (TOS: "Mudd's Women")
When Leonard McCoy, Hikaru Sulu and Nyota Uhura were trying to choose a program in Enterprise's rec room in 2270, McCoy said he was in the mood for a walk in the woods. The others agreed. (TAS: "The Practical Joker")