What is the meaning of Spontaneous?

Self-generated; happening without any apparent external cause.

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

Proceeding from natural feeling or native tendency without external or conscious constraint.

Arising from a momentary impulse.

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.

Source: wiktionary.org