The most popular social media platforms are Facebook, Instagram, Twitter, YouTube, and TikTok.

Facebook: With over 2.8 billion monthly active users, Facebook is the largest social media platform in the world. It allows users to connect with friends and family, share updates, photos, and videos, and join groups and communities.

Instagram: Owned by Facebook, Instagram has over 1.2 billion monthly active users. It is a visual-based platform that allows users to share photos and videos, and has become increasingly popular for businesses and influencers to promote their products and services.

Twitter: With over 330 million monthly active users, Twitter is a microblogging platform that allows users to share short updates, known as tweets, and engage in real-time conversations. It is widely used by politicians, celebrities, and journalists.

YouTube: With over 2 billion monthly active users, YouTube is the largest video-sharing platform in the world. It allows users to upload, share, and view videos, and has become a popular platform for vloggers, content creators, and influencers.

TikTok: With over 1 billion monthly active users, TikTok is a short-form video-sharing platform that allows users to create and share 15-second videos, often set to music. It has become particularly popular among younger generations and has become an important platform for influencer marketing and brand promotion.

Note that these are the most popular platforms at the moment and the ranking may change over time, as well as the number of users.