Capitalize/ˈkæpɪtəlaɪz/ Definition 1 of 4Pro Tip 1/3First Letter Capitalize the first letter of a sentence or a proper noun like someone's name. Her name is Ann. Pro Tip 2/3Titles and Headings Each significant word in titles and headings should be capitalized. The article's title is 'Advances in Renewable Energy'. Pro Tip 3/3Acronyms Acronyms are fully capitalized to stand out as abbreviations of phrases. NASA stands for National Aeronautics and Space Administration.