The term is often used when on thyroid testing, there is mild elevation of TSH. The patient may be asymptomatic if thyroid testing has been done as part of screening or there may be mild symptoms of hypothyroidism. Also referred to as subclinical hypothyroidism, a condition for which there is a lot of controversy whether it should be treated or not.
Hypothyroidism, also called underactive thyroid or low thyroid, is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone.
I have not heard the term "Biochemical hypothyroidism" before, but it must be an alternative for "Functional", "Subclinical" "Metabolic" or "Intracellular" hypothyroidism.
I prefer to use the term "Intracellular hypothyroidism", because it describes the condition more clearly.
For an in-depth explanation of the malady, see
https://cbhrt.ca/hormone-therapy/ ..... read the page entitled "The thyroid hormone and Intracellular hypothyroidism"