Capitalization means using capital, or upper-case, letters. Capitalization of place names, family names, and days of the week are all standard in English.
Using capital letters at the start of a sentence and capitalizing all the letters in a word for emphasis are both examples of capitalization. Capitalization also means the act of gaining an advantage from some opportunity: "Her capitalization of the voters' frustration made it much easier for her to win the election." The earliest meaning, however, was purely financial, from the sense of capitalize that means "convert financial assets to capital."