The phrase "outbound leg" refers to the first part of a journey or trip, when a person or thing is going away from a starting point or origin. Full definition
And although the coffee on the early outbound leg Friday morning was atrocious (bad water, I think) with no time for breakfast, I was able to grab a cappuccino, yogurt, fruit, and cereal at the club instead of going to Starbucks. (travelcodex.com)
Making the journey to Hawaii for a 10 day holiday, our final outbound leg would be aboard Alaska Airlines from San Diego to Honolulu. (benjaminjtravel.com)
The new view was obtained on July 10, 2016, at 10:30 a.m. PDT (1:30 p.m. EDT, 5:30 UTC), when the spacecraft was 2.7 million miles (4.3 million kilometers) from Jupiter on the outbound leg of its initial 53.5 - day capture orbit. (sciencedaily.com)