Reliability is an Assessment that someone will do what they promised to the agreed standard. It is one component of Trust.
It differs from Competence because Reliability is “will they”, whereas competence is “can they” In my career I have worked with many highly-competent, yet unreliable people.
Compensating for a lack of Reliability means extra effort is required on my part.
Unreliability in one domain of life does not mean unreliability in all.