What is the meaning of Spontaneous?

Self-directed; happening or acting without external cause or instigation; proceeding from natural feeling, temperament, or momentary impulse.

Done by one's own free choice, or without planning.

Controlled and directed internally; self-active; spontaneous movement characteristic of living things.

Produced without being planted or without human cultivation or labor.

Sudden, without warning.

Said or done without prior planning or prior writing.

Source: wiktionary.org