A "true seed" in basketball is a term used to set the field of teams for a tournament (more specifically, March Madness). A team's true seed refers to their place in the overall seeding of an entire tournament, not just their seed from a regional.
True seeds may be better understood by the terms "seed list," "overall seed," or "field of 68."
In order to completely understand the concept of a true seed, one must understand the entire selection process. There are four steps that the selection committee takes in this process: initial balloting, selection, seeding, and bracketing.
Once the committee assigns each team a true seed, they then sort the teams into each region based on their true seed (for example, the top four true seeds will become the four 1-seeds, with one in each region). The idea is that higher-seeded teams have earned the right to play in their geographic region, where they will be closer to home.
True seeds are also used to determine the participants of the First Four. These play-in games are held in the two days before the first round begins, and the four winners advance to complete the field of 64.
The four at-large teams with the lowest true seeds are the 11-seeds of the First Four, while the four lowest automatic-qualifying teams become the 16-seeds. In the First Four, the 11-seeds are more likely to be major-conference programs or well-known mid-majors, while the 16-seeds are usually lesser-known automatic qualifiers from weaker conferences. Regardless of how they got there, all the teams in the First Four are usually grateful to even have a chance at making it into the tournament.