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.
Some people use the term swollen glands to refer to swollen lymph nodes, especially when the nodes in the neck are swollen. However, lymph nodes are not glands. Lymph nodes in only one body area may be swollen, or nodes in two or more body areas can be swollen. Other symptoms, such as sore throat, runny nose, or fever, may be present depending on the cause. Sometimes swollen lymph nodes are discovered when the person is being examined because of another symptom.