Nodules are abnormal growths in the thyroid. A few cells of the thyroid multiply abnormally and form a small lump in the substance of the thyroid. They may even have a cover (called capsule) which makes them separate from rest of the thyroid gland. A gland may have more than one nodule: it is then called multinodular goiter. Although more than 90 % of the nodules are benign, some of the nodules may be malignant (cancerous).
Some of these nodules are solid and some have fluid(cystic) and some are a mixture of both. Some are small and are not identified outside, but some may become big enough to obstruct breathing and swallowing. Some of them produce thyroid hormones and this can make the person hyperthyroid. Any growth of the thyroid is called a goiter.