Definitions:

1. The habit or practice of giving opinions and advice beyond one's knowledge or expertise. NOUN
   • The article was filled with ultracrepidarianism, offering medical advice without citing any experts.
2. The tendency to speak with authority on topics one doesn't understand. NOUN
   • His ultracrepidarianism was frustrating- he spoke confidently about topics he clearly didn't understand.

Synonyms:

• overconfidence
• presumptuousness
• pseudo-expertise