These are an extremely common clip used on the majority of Honda models since 1992. They are normally used to attach bumpers or side skirts but also engine undertrays and sill mouldings. The Civic also uses this clip to fix the grille / landing panel cover.
The Honda part number is 91503-SZ3-003.
Although they are sold here as Honda clips, these parts are also used by Toyota and would be suitable for many other purposes.
Please make sure to check the dimensions before purchasing to see if they will be suitable for your needs.