What was the name of the student game that inspired the portal mechanic?

The student game that inspired the portal mechanic was called Narbacular Drop.

Narbacular Drop was a 2005 puzzle-platform game created by students at DigiPen Institute of Technology. Its central idea was a pair of linked portals that let the player move through space in unconventional ways. The game also allowed portals on surfaces such as walls, floors, and ceilings, establishing a foundation for Portal's spatial puzzles.

Valve became interested after the student team presented the project, and the developers were hired to work at Valve. Many of the same designers went on to create Portal, which kept the core portal concept while adding Chell, GLaDOS, the Aperture Science setting, and a more polished first-person format.

DigiPen was the school where the game was made, not the game's title. Tag: The Power of Paint was another student project that influenced Portal 2's gel mechanics, while The Lab is a separate Valve game.