In texting and writing, SMH stands for 'shaking my head'. The term expresses disappointment, embarrassment, or bafflement regarding a specific topic or piece of information. If someone responds to a text or tweet with 'SMH', they're expressing disappointment at the content of the message.
Internet slang comes and goes, but some terms stick around for years. One such example is the abbreviation SMH, which you'll see appearing in tweets, instant messages, texts, and status updates.
People also tweak SMH slightly to add emphasis. The most common form of this is SMDH, which stands for 'shaking my damn head'. But you can also find other examples such as SMFH, with the F being a common curse word.
Another less common meaning of SMH, is 'so much hate'. However, this usage is relatively rare. You should be able to tell by the context of a message. But when in doubt, 'shaking my head' is the dominant (and therefore most likely) meaning.
How is SMH used?
SMH is often used on social media platforms in tandem with GIFs depicting someone else… shaking their head.
GIFs, or Graphics Interchange Format, are animated images that are often used with text.
GIFs of celebrities or well-known characters work well with the abbreviation SMH, usually done to be funny.