"Hypoechoic" means it appears darker on the ultrasound than the surrounding tissue. Hypoechoic when used to describe a single thyroid nodule compared to surrounding tissues has a higher probability of being malignant, however, when the entire thyroid gland is described as hypoechoicit often indicates an inflammatory thyroid disease such as Graves or Hashimoto's.
Heterogeneous echotexture is usually found in patients with Graves or Hashimoto's as well. That just means the overall texture of the gland varies and is not "isoechoic" or the same throughout.
Lobular contour is referring to the outside surface of the thyroid gland. Normal, healthy thyroids have a smooth appearance, lobular means it is more irregular, again, this is found in people with Hashimoto's or Graves.
Nodules are usually benign but sometimes can be cancerous. If there were nodules, depending on size and texture, further investigation may be needed. In this case, no nodules is good.
Size seems a little small, if this is an adult thyroid. It is possible it is shrinking compared to previous measurements, however, dimensions can vary from ultrasound to ultrasound and I would not rush to conclusions since none of those dimensions are that far off from the previous measurements.
Doppler flow refers to the movement of blood through the thyroid gland. It can sometimes be used to distinguish between Graves and Hashimotos/thyrotoxicosis, as it is usually higher flow in Graves compared to other thyroid conditions.
Without any other information, such as symptoms, many of these ultrasound characteristics are found in people with an autoimmune thyroid disease such as Hashimoto's or Graves. Hashimoto's frequently causes hypothyroidism symptoms (too little thyroid hormone), Graves causes hyperthyroidism (too much thyroid hormone).
I'm not a medical expert and don't know what small thyroid size means, especially in relationship to the other thyroid characteristics. Often with Hashimoto's or Graves, people may have an enlarged thyroid, especially as the disease progresses.
Sarah described your report very well.
Although our thyroid can become swollen/enlarged with Hashimoto's, over time, Hashimoto's can also cause our thyroid to shrink. It's also common for the thyroid to shrink as we age.
You don't say what your age is, whether there are symptoms of thyroid malfunction, whether you're currently taking a replacement thyroid hormone medication, etc.
Have you had any other tests done, such as thyroid function blood work, which should include Free T4 and Free T3 (actual thyroid hormones) along with TSH, which is a pituitary hormone. It's often advantageous to have thyroid antibody tests done, as well to test for Hashimoto's or Graves Disease.