recommendation
This word carries a weight of trust and endorsement. It is not a mere suggestion, which can be casual or whim-based, but implies that the person speaking has a reason—either through expertise or personal experience—to vouch for the quality of the object or person.
In professional settings, the term takes on a formal, almost legalistic quality where a recommendation serves as a credential. In consumer contexts, it functions as a social shortcut to avoid risk, shifting the responsibility of quality from the buyer to the recommender.
Countable when referring to a specific piece of advice or a written letter. Uncountable when referring to the general act of suggesting things to others.
Meanings
A suggestion or proposal that something is good or suitable for a particular purpose.
I followed my friend's recommendation and bought the book.