Is stereo a proper noun or pronoun?

The Word 'stereo' is not a proper noun or a pronoun. The Word 'stereo' is a common noun, a Word for any stereo of any kind, anywhere.

A proper noun is the name of a specific person, place, or thing; for example:

• Blaupunkt Car Stereo Speakers and Receivers
• Stereo Plus (retail store), Las Vegas, NV

A pronoun is a Word that takes the place of a noun in a sentence. The pronoun that takes the place of the noun stereo is 'it'. Example:

• The stereo is new, it was a gift.