Final answer:
Chronic diseases are characterized by periods of remission and exacerbation. They are long-term conditions that can have periods of worsening symptoms followed by periods of improvement or absence of symptoms.
Step-by-step explanation:
The type of illness characterized by periods of remission and exacerbation is a chronic disease. Unlike an acute disease, which is short in duration with a rapid onset, a chronic disease lasts for months or years and may exhibit periods where symptoms become more or less severe. A chronic disease can have recurring flare-ups, known as exacerbations, followed by times when the symptoms diminish or disappear, known as remissions. An example of such a disease is Type 1 diabetes, where the condition is managed over a lifetime and symptoms can be controlled.