Subtitles can be either interlingual (going from one language to another) or intralingual (where the language of the subtitle file is the same as the language of the video it relates to). Generally speaking at Netflix, subtitles are interlingual timed text assets and SDH/CC are intralingual assets.
SDH (subtitles for the deaf and hard of hearing) and CC (closed captions) are both intralingual and close in form, contents and purpose but have some key differences. Both file types are intended to support the viewing needs of people who cannot hear the audio fully - the files replicate dialogue, music and sounds in text form - but differ in terms of technical spec and style.
“Closed captioning” is a legacy term for broadcast captions in the US which have a lower characters per row allowance, as well as different display mechanisms and formatting options compared to traditional subtitling. As a term, “SDH” can be defined as a mix between subtitles and captions in that they are stylistically and technically the same as subtitles but have the same intended audience and contents as CC.
At Netflix, subtitles and SDH are produced for offline branded content, not closed captions, but you may hear people using SDH and CC interchangeably.