What is the difference between hyperthyroidism and thyroiditis.?

Latter to former. Thyroiditis is a general term applied to the condition whereby the thyroid gland is inflammed, usually by the body's own immune system. Such reaction can lead to transient rise in thyroid hormone levels causing hyperthyroidism followed by a state of low thyroid, also called hypothyroidism. Some individuals can have high thyroid output from the start and stay longer until an intervention is made.
Yes. Thyroiditis means inflammation of the thyroid and the thyroid function may end up normal, high, or low often depending on the stage. Most will end up with hypothyroidism even though there may be an initial phase of hyperthyroidism. Thyroiditis is like the hen which may or may not lay an eggl.