General meaning:
* Guhit na pahilis: This literally means "slanted line." It's a general term for a line that's not horizontal or vertical.
* Guhit sa ilalim: This means "line under." It's a more specific term for a line drawn under something.
Specific uses:
* Pangkat ng titik: This means "group of letters." You can use this when talking about underscores used in filenames or code.
* Tanda ng paghihiwalay: This means "separation mark." This refers to the underscore's function as a delimiter.
Ultimately, the best translation for "underscore" will depend on the specific context.
It's always a good idea to explain what you mean using a phrase like "ang guhit na nasa ilalim ng pangalan" (the line under the name).