What is difference between voiced and lenis consonants in English language.
The terms reflect personal terminological preferences regarding certain consonants in English. "Voiced" usually refers to a physical property, that the vocal folds are vibrating during the production of the sound. This is clearly the case of [æ] in "man", but not clear in the case of b. The alternative terms "fortis" and "lenis" are therefore applied to some sounds of English, thus b can be called "lenis" thereby avoiding the particular phonetic claim of the term "voiced". The putative phonetic correlate of "lenis" is "relatively less energy".
This terminological problem arises because certain English sounds like /g/ – voiced stops – are not consistently produced with vocal fold vibration, as contrasted with their production in languages like French. When an analyst calls /b/ a "lenis" stop (or plosive), they are still very unlikely to call /m/ lenis (except in special circumstances). The term "lenis" is much broader than "voiced".
One problem is that there is no phonetic unity to "lenis" consonants – that's not actually a measurable physical property. Instead, it is a special term for a phonological distinction in consonants which is not phonetically-based. In substance-free theories of phonology, terms like "voiced" are anyhow devoid of necessary phonetic characteristics, so the terms used for English are indeed entirely arbitrary.