From Halopedia, the Halo wiki
Explorer was a career award found on the web version of Halo Waypoint from 2009-2014 and on the Xbox 360 version until its discontinuation in 2022. It was represented by a flag on a circular medal with a black and gold ribbon. The award consisted of 38 achievements related to exploration (ie. Easter eggs and unlockables). These achievements were organized into eight tiers.