The term "alto" in science usually refers to a high altitude. This is especially common in meteorology where it describes weather phenomena happening at high altitudes.

Here are some examples:

* Altocumulus clouds: These are middle-level clouds that appear as white or gray patches arranged in layers or sheets.

* Altostratus clouds: These are also middle-level clouds that appear as a sheet-like veil covering the sky.

* Altostratus lenticularis: These are lens-shaped clouds that form over mountains.

It's important to note that "alto" can also be used in other scientific fields. For example, in astronomy, it could refer to something high in the sky, like an altocumulus cloud, or a high-altitude region of the atmosphere.

However, without context, it's difficult to give a definitive meaning for "alto" in science. If you provide more information about the specific context where you encountered this term, I can provide a more precise answer.