A joint-stock company is a business entity which is owned by shareholders. Each shareholder owns the portion of the company in proportion to his or her ownership of the company's shares (certificates of ownership). This allows for the unequal ownership of a business with some shareholders owing a larger proportion of a company than others. Shareholders are able to transfer their shares to others without any effects to the continued existence of the company.

SPA can refer to:

• SPA (band), a 1990s British band

The term spa is associated with water treatment which is also known as balneotherapy. Spa towns or spa resorts (including hot springs resorts) typically offer various health treatments. The belief in the curative powers of mineral waters goes back to prehistoric times. Such practices have been popular worldwide, but are especially widespread in Europe and Japan. Day spas are also quite popular, and offer various personal care treatments.

Spondyloarthropathy is any joint disease of the vertebral column. Spondyloarthropathy with inflammation is called spondylarthritis. In contrast, spondylopathy is a disease of the vertebra itself, but many conditions involve both spondylopathy and spondyloarthropathy. In the broadest sense, the term spondyloarthropathy includes joint involvement of vertebral column from any type of joint disease, including rheumatoid arthritis and osteoarthritis, but the term is often used for a specific group of disorders with certain common features, the group often being termed specifically seronegative spondylarthropathies. They have an increased incidence of HLA-B27, as well as negative rheumatoid factor and ANA. Enthesopathy is also sometimes present in association with seronegative spondarthritides. Nonvertebral symptoms of spondyloarthropathies included asymmetic peripheral arthritis (which serves as an important distinguishing factor with rheumatoid arthritis), arthritis of the Toe IP Joints, sausage digits, achilles tenosynovitis, plantar fasciitis, costochondritis, iritis, and mucocutaneous lesions. However, lower back pain is the most common clinical presentation of the disease; this back pain is unique because it decreases with activity.