Where does “Székely Land” come from?

Székely Land (English) comes from Hungarian Székelyföld, from Hungarian Székely, from Hungarian székely — Székely.

Ancestry of “Székely Land”, step by step

Step	Language	Word	Meaning
1	Hungarian	Székelyföld	—
2	Hungarian	Székely	—
3	Hungarian	székely	Székely