"Jurisdiction of the subject matter of a suit can not be conferred by agreement or consent, or be waived or `based on an estoppel of a party to deny that it exists.'" Langston v. Nash, 192 Ga. 427, 429 ( 15 S.E.2d 481). "A judgment which is void for want of jurisdiction does not afford any basis for applying the doctrine of res adjudicata or estoppel. Dix v. Dix, 132 Ga. 630 (3) ( 64 S.E. 790). Nor does the fact that the husband did not except to the original judgment for alimony, and made the ordered payments for eight months, affect the result.

See also Deen v. Baxley State Bank, 192 Ga. 300 ( 15 S.E.2d 194), where this court, after stating the rule that "the superior court has power during the same term at which an order or judgment is rendered, to revoke or vacate it for meritorious cause", held that "[s]uch power is not lost during the term merely because the time for excepting to the judgment directly by writ of error has expired." See also Seigler v. Seigler, 181 Ga. 310 ( 181 S.E. 822); Langston v. Nash, 192 Ga. 427 ( 15 S.E.2d 481); Eagan v. First National Bank, 212 Ga. 212, 213 ( 91 S.E.2d 499). Applying that rule to the plaintiff's contention that the judgment here had become final, and that the question was res judicata and the judgment could not be set aside, the contention is clearly without merit. 3. "The judgment of a court having no jurisdiction of the person or subject-matter, or void for any other cause, is a mere nullity, and may be so held in any court when it becomes material to the interest of the parties to consider it."

When a court has before it a matter where it has no jurisdiction of the subject matter, no legal judgment can be rendered except one of dismissal; and when this court discovers from the record on appeal that a judgment has been rendered by a court having no jurisdiction of the subject matter, it will of its own motion reverse the judgment. Smith v. Ferrario, 105 Ga. 51, 53 ( 31 S.E. 38); Langston v. Nash, 192 Ga. 427, 429 ( 15 S.E.2d 481); Ethridge v. Echols, 212 Ga. 597 (2) ( 94 S.E.2d 377); Sweatman v. Roberts, 213 Ga. 112, 113 ( 97 S.E.2d 320); Williams v. Kaylor, 218 Ga. 576, 581 ( 129 S.E.2d 791). 3. The judgment granting custody of the minor children to the father is reversed, with direction that the question of custody be returned to the Superior Court of Fulton County for hearing and determination.

"Jurisdiction of the subject matter of a suit cannot be conferred by agreement or consent, or be waived or based on an estoppel of a party to deny that it exists." Langston v. Nash, 192 Ga. 427, 429 ( 15 S.E.2d 481); Georgia R. Bkg. Co. v. Redwine, 208 Ga. 261, 262 ( 66 S.E.2d 234). It follows that the trial court had no jurisdiction of this case at the subsequent term of court after its final judgment had been entered. Its order on that date was void.

A judgment which is void for want of jurisdiction of the subject matter will not afford any basis for applying the doctrine of res judicata. Langston v. Nash, 192 Ga. 427, 430 ( 15 S.E.2d 481). The court erred in sustaining the plea of res judicata.

However, the judgment now claimed to be res judicata was rendered by a court which lacked jurisdiction of the subject matter and, for that reason, was not res judicata. See such cases as Dix v. Dix, 132 Ga. 630 (3) ( 64 S.E. 790), and Langston v. Nash, 192 Ga. 427, 430 ( 15 S.E.2d 481). Juvenile courts are courts of limited jurisdiction.

Jurisdiction of the subject matter "can not be conferred by agreement or consent, or be waived or `based on an estoppel of a party to deny that it exists.' Parker v. Travelers Insurance Co., 174 Ga. 525, 529 (163 Se 159);. . . " Langston v. Nash, 192 Ga. 427, 429 ( 15 S.E.2d 481); Rainey v. McRae, 14 Ga. 589 ( 60 AD 660); Kantzipper v. Kantzipper, 179 Ga. 850 ( 177 S.E. 679); Mathis v. Rowland, 208 Ga. 571 ( 67 S.E.2d 760); Sweatman v. Roberts, 213 Ga. 112 ( 97 S.E.2d 320). However wrong Della Jane Turner's conduct may have been in removing her child from Gwinnett County to Fulton County without authority, she is the mother of the child and was living in Fulton County where she was caring for her child.

Dix v. Dix, 132 Ga. 630 (3) ( 64 S.E. 790). Nor does the fact that the husband did not except to the original judgment for alimony, and made the ordered payments for eight months, affect the result. Seigler v. Seigler, 181 Ga. 310 ( 181 S.E. 822); Jones v. Jones, supra; Langston v. Nash, 192 Ga. 427 ( 15 S.E.2d 481). The decree for permanent alimony being void for the reasons above stated, it was not error for the court to vacate the order directing issuance of a fi. fa. for the amount alleged to be due under the decree, and to direct cancellation of the fi. fa. and the record of the same.

The agreement would not confer jurisdiction upon Fulton Superior Court because jurisdiction of the subject matter of a suit cannot be conferred by consent, waiver, or be "based on an estoppel of a party to deny that it exists." Langston v. Nash, 192 Ga. 427, 429 (2) ( 15 S.E.2d 481), and cases cited. Also see Stallings v. Bass, 204 Ga. 3 ( 48 S.E.2d 822).

It may be waived, however, as to the person, so far as the rights of the parties themselves are concerned; but not so as to prejudice third persons." Raney v. McRae, 14 Ga. 589 (4) (60 Am. D. 660); Adams v. Lamar, 8 Ga. 83 (3); Ponce v. Underwood, 55 Ga. 601; Yon v. Baldwin, 76 Ga. 769; Block v. Henderson, 82 Ga. 23, 25 ( 8 S.E. 877); Stevens v. Nisbet, 88 Ga. 456 ( 14 S.E. 711); Rosenthal v. Langley, 180 Ga. 253, 260 ( 179 S.E. 383); Langston v. Nash, 192 Ga. 427, 429 (2) ( 15 S.E.2d 481); Black v. Milner Hotels, 194 Ga. 828, 831 ( 22 S.E.2d 780). 4.