Capital letters and Upper-case letter

Upper-case letter and capital letters are semantically related. In some cases you can use "Upper-case letter" instead a noun phrase "Capital letters".

Upper-case letter noun - One of the large alphabetic characters used as the first letter in writing or printing proper names and sometimes for emphasis.

Capital letters and upper-case letter are semantically related. Sometimes you can replace phrase "Capital letters" with "Upper-case letter", this phrases are similar.