A suspended chord, which is commonly abbreviated as "sus chord", is a triad chord where the third (either major or minor) is omitted.
For a suspended second chord, the third is replaced with a major second.
The chord has an open sound due to the left out third but also conveys tension because of the dissonance between the root and the second.
Below, you can find a list of all suspended second chords available on ChordAtlas. Clicking on the respective entry will lead to the detail page of the selected chord: