It is a self-regulating process by which biological systems maintain stability while adjusting to changing conditions.

Not the earlier 1926 reference, but a 1929 Cannon article using the term homeostasis is online (as at November 15, 2024):

https://journals.physiology.org/doi/pdf/10.1152/physrev.1929.9.3.399

Cannon, Walter B. Organization for Physiological Homeostasis 1929-07-01 Physiological Reviews , Vol. IX, No. 3 p. 399-431

The wisdom of the body by Walter B. Cannon, Publication date 1932 is on archive.org; there are three copies.

At page 24: " ... I have suggested a special designation for these states, homeostasis. The word does not imply something set and immobile, a stagnation. It means a condition—a condition which may vary, but which is relatively constant."

So far I have had no luck finding a copy of the book, a festschrift for Charles Robert Richet, that includes Walter B. Cannon's 1926 article, "Physiological Regulation of Normal States: Some Tentative Postulates Concerning Biological Homeostatics." 500 copies of the booklet were printed.

I found a copy of one page of his article, which is page 91 of the booklet containing the essays in honor of Richet by various contributors.

Page 91, the first page of Cannon’s contribution, contains the first definition of homeostasis:

“The steady states of the fluid matrix of the body are commonly preserved by physiological reactions, i. e., by more complicated processes than are involved in simple physico-chemical equilibria. Special designations, therefore, are appropriate: - « homeostasis » to designate stability of the organism ; « homeostatic conditions », to indicate details of the stability; and « homeostatic reactions », to signify means for maintaining stability.”