The acronym HDMI stands for: High-Definition Multimedia Interface.
HDMI ports on a television are used to connect game consoles, Bluray, DVD or hard drive players, stereos, Chromecast, Fire TV Stick, Apple TV, Android TV Box or any other "stick" for video on demand playback.
The HDMI connection includes high definition video and audio in the same cable, from versions 1.0 to 1.3a they only support 2k video, however from version 1.4 support for 4k resolution was included (4096 × 2160 at 24 Hz) in addition to a channel to be able to include or share an internet connection.
The latest version of HDMI to date is 2.1, released in 2017 and including numerous improvements such as a maximum resolution of 10K at 120 Hz.
Today it is becoming common to have an old game console such as a PlayStation 3, PlayStation 4 or Xbox (or all of them), a DVD or Bluray player and an HDMI stick, Android TV Box or hard drive connected to the television and it is necessary that our TV has a sufficient number of HDMI connections to avoid plugging and unplugging cables, you can have them all connected and well organized and hidden.
HDMI is currently the default video and audio transmission interface in televisions, therefore it is important to have enough ports since all external devices are prepared to use this type of connection.