Objectives are the main goals to achieve by the end of a run strategy or social media campaign. Objectives can be a part of your marketing strategy, your content strategy online, or an advertising campaign on social media.
Objectives in an advertising campaign can be different for different social media platforms as a set of goals that an ad would target. Different social media platforms hold different objectives and platform-centric objectives as well.

Example

For Facebook Ads, objectives are divided into three categories: Awarness, Consideration, and Conversions. These objectives help format an ad and the amount it might cost you to achieve them.