A typical dental check-up has two parts
Part one, by the dentist, is the visual examination, evaluation, diagnosis, and recommendations best suited for your needs.
Part two, by the dental hygienist, is the taking of any X-rays that may be required, teeth cleaning, polishing, plaque and tartar removal, periodontal (gum) probing, and oral hygiene instructions.
Some terminology that you may come across during your routine hygiene appointment are probing and ultra-sonic scaler. Ultra-sonic scaler is a dental instrument for removing sticky plaque and hard tartar from your teeth. Previously, dental hygienists used hand metal dental instruments to scrape teeth. They still do some of that, but the job is made much easier on you (and on them) by the use of an ultra-sonic scaler, which breaks down the bacterial cell walls that are responsible for the stickiness of plaque.
Periodontal Probing is measuring of the depth to which a probe can travel between the tooth and gum, an indicator of your gum health. The hygienist uses a periodontal probe to measure the depth of gum pockets and compare the new measurements to previous measurements to see if the pockets are getting deeper. If periodontal disease has already progressed, x-rays are used to see and compare with the previous ones to make a diagnosis.