Hangul syllable ddya

Turn on Korean input, press Shift+E, then I.

On the standard Korean keyboard layout — Dubeolsik — Shift+E enters the tense consonant ㄸ and I enters the vowel ㅑ; the input method joins them into one syllable block. The Latin labels ddya and ttya help a search find the name, but they do not type the character.

What does 땨 mean?

It spells a sound — ttya — not a standalone idea.

땨 is pronounced as a tense, pressed t followed by ya; standard Korean romanization writes the sound ttya. The block joins ㄸ and ㅑ with no final consonant, so it only contributes a syllable sound; which word it lands in decides the meaning.

Hangul was created so people could write Korean without first learning Chinese characters; its creation and explanatory manual date to 1443 and 1446, and 땨 is one block that system can assemble.

Why does 땨 start with ㄸ?

ㄸ is the tense twin of plain ㄷ.

Doubled consonant letters such as ㄸ already existed in the 15th century, when they helped transcribe the sounds of Chinese characters; since the 20th century they have marked Korean's tense consonants — harder, pressed versions of the plain sounds.

If 땨 looks different across devices, that is the font, not a different character — Unicode's chart glyph is only representative.