Definitions:
Tendonitis – inflammation of tendon ( can be Achilles tendon, patellar tendon, elbow tendon, wrist tendon, shoulder tendons aka the rotator cuff),
Tenosynovitis – inflammation of the gliding surface of the tendon and the surrounding sheath; Sheathed tendons are usually found in the wrist and ankles where tendons pass close to the bone.
Calcific tendonitis – calcium deposits in tendon usually from chronic inflammation

Signs/Symptoms– persistent pain, referred pain, pain decreases after warming up, pain increases after use, muscle weakness may occur, common with strains and sprains heat, swelling, stiffness usually in musclo-tendinous junction because of weakness and limited blood supply there

Causes: over use of tendon/muscle, tendon/muscle is not strong enough to do the requested movements, misalignment of posture causing more wear and tear on specific areas
Treatment Guidelines:

decrease pain and swelling break up adhesions
triggerpoint injured area and surrounding areas
realign and balance posture
deep tissue work to muscles of the tendons to relieve pressure
ice massage or vascular flush (alternating hot and cold, ending in cold)
light stretching
exercise to strengthenCommon types: Achilles tendonitis, patellar tendonitis, rotator cuff tendonitis, infraspinatus tendonitis, tennis elbow, shin splints, repetitive stress syndromes (RSI)

Resources:

When Is It Tendinitis? By Whitney Lowe, LMT, NCTMB

Types of Tendon Injury By Whitney Lowe, LMT, NCTMB

Friction Massage Therapy A simple self-massage technique helpful in resolving tendinitis by Paul Ingraham, Registered Massage Therapist (Vancouver)

Deep transverse friction massage for treating tendinitis Brosseau L, Casimiro L, Milne S, Robinson V, Shea B, Tugwell P, Wells G. Pub Med

Tendinitis Masquerading as Knee Joint Pain By Ben Benjamin, PhD

Weakness and Tendon Injuries By Ben Benjamin, PhD

Google Books:

Understanding Sports Massage – Patricia Benjamin