Et al. is an abbreviation for et alia (neutral), et alii (masculine) or et aliae (feminine). When translated from Latin, it means “and others”. Etc. is an abbreviation for et cetera (commonly written without the space in English), translated from Latin as “and the rest”. The literal Latin translation for inter alia is “among other things”.
Et al. is used at the end of a list of proper nouns to indicate additional proper nouns, e.g., John, Jane, Sue, et al. are coming to the party. Etc. appears at the end of a list to indicate additional things that are similar, e.g., cheddar, Monterey jack, swiss, etc. Inter alia is typically used in legal documents, e.g., The judge stated, inter alia, that the defendant was guilty.