Small Capitals (smcp) turns lowercase letters into glyphs that resemble uppercase letterforms but reduced in size, close to the surrounding lowercase letters.
Small Capitals are not simply scaled-down versions of normal capitals. They normally retain the same stroke weight and have a wider aspect ratio to harmonize with surrounding letters, both uppercase and lowercase ones.
Small Capitals are used in running text as a form of emphasis alongside italic and bold, for example to draw attention to the openning phrase of an article. They are also used where uppercase letters would appear jarring, like in long acronyms.