Refers to one's firmly held personal belief or conviction, often used in formal or public statements.
彼は所信を述べた。
He stated his conviction.
The new mayor stated his convictions soon after taking office.
所信表明演説で首相は政策の方向性を示した。
In his policy speech, the prime minister indicated the direction of his policies.
The chairperson expressed his views at the start of the meeting.
意見 is a neutral word for an opinion on a topic, whereas 所信 conveys a deeper personal conviction usually expressed in formal contexts.
general policy speech
Compound of 所 (place, basis) and 信 (belief, trust), literally 'where one's belief is based'.