Endogenous: originating within (the body). Refers to hormones, enzymes, or other bioactive chemicals produced within the patient's body. Opposite of exogenous.
In the case of type 2 diabetes, the body is producing some endogenous insulin; the problem is that it's not enough for the body's requirements, or the system is unable to utilize it properly. With type 1 diabetes, the body is not producing insulin, thus it must be replaced from outside of the body with insulin injections.
Certain endogenous steroids can create problems with diabetic regulation. One example is the naturally occurring hormones of menstrual cycles/heat and/or pregnancy in unspayed female animals. Other examples are the excess of endogenous cortisol arising from Cushing's disease, the excess endogenous thyroid hormones of hyperthyroidism, and the excess growth hormone of acromegaly.