I believe they mean that the random variables have a common support. For example, if X ~ Unif[0,2] and Y ~ Unif[1,3], then their respective PDF's overlap in the interval [1,2], meaning the only interval where both X and Y can have common values is [1,2]. To illustrate, below is a representation of the supports of X and Y, below which is a representation of the real line.
1 Thyroid cancer is a malignant tumor of the thyroid gland. 2  Symptoms of thyroid cancer include swelling in the neck (goiter), neck pain, hoarseness, swallowing and breathing problem, swollen lymph gland in the neck.
Thyroid cancer can cause any of the following signs or symptoms: A lump in the neck, sometimes growing quickly. Swelling in the neck. Pain in the front of the neck, sometimes going up to the ears. Hoarseness or other voice changes that do not go away. Trouble swallowing. Trouble breathing.