Homographs are words that are spelled the same but that have different meanings, usages and pronunciations. For example, the word "close" can mean shutting down something when the "s" is pronounced as a "z" or being near something when the "s" is pronounced as an "s." Homographs and heteronyms are often confused because they are similar. However, only the homograph has the capacity to sound the same.
Heteronyms are words that are spelled exactly the same but have different meanings when they are pronounced differently. Heteronyms are distinguished by accenting different parts of the same word. For example, the word "lead" can be pronounced with an accent on the "ea" to mean guiding or taking charge, but when putting the emphasis on the "d," it means the metallic element.
Homonyms are words that have the same spelling and pronunciation, but have different meanings. The word "bow" is an example because it can mean a ribbon placed on top of a gift, it can be the bow of a ship, or it can be the instrument used to propel arrows. In the case of homonyms, when written and spoken, a context is needed to associate the correct definition to the word in question.
Homophones are words that are pronounced the same but differ in meaning and spelling. For example, the words "pear" and "pair" sound the same when spoken, but one is a fruit while the other refers to a combination of two elements. When written, homophones are not mistaken for each other, but when spoken, a context is needed to understand which definition is correct.