The two types of semiconductors. N-types have a slight excess of electrons, allowing them to move freely and P-types have a slight lack of electrons, effectively making freely moving electron “holes”. By sandwiching them next to each other, you can create diodes and bi-polar junction transistors.

And as we all know, bi-trans is an important part of queerdom.

Source: has a degree in electrical engineering. And is bi.
Edit: not cool enough to be trans though.