Boiled eggs are eggs (typically chicken eggs) cooked with their shells unbroken, usually by immersion in boiling water.
Hard-boiled eggs are cooked so that the egg white and egg yolk both solidify, while for a soft-boiled egg the yolk, and sometimes the white, remain at least partially liquid.
Hard-boiled eggs are commonly sliced, particularly for use in sandwiches.
For this purpose specialized egg slicers exist, to ease slicing and yield even slices.
Hard-boiled eggs should be used within two hours if kept at room temperature or can be used for a week if kept refrigerated and in the shell. (source)
Can guinea pigs eat hard boiled eggs?
If they nibble them they will be fine, but they shouldn’t be purposely fed as part of a regular diet.
They have no nutritional benefit for guinea pigs and eating a lot may make them sick.
For more foods that guinea pigs can and can’t eat check out our guinea pig food list