Before we give an answer to the question, it would be in order if we recount the story. Here it is:
Jg 11:30 And Jephthah made a vow to the LORD, and said, "If You will indeed deliver the people of Ammon into my hands,
31 "then it will be that whatever comes out of the doors of my house to meet me, when I return in peace from the people of Ammon, shall surely be the LORD'S, and I will offer it up as a burnt offering."
Jg 11:32 So Jephthah advanced toward the people of Ammon to fight against them, and the LORD delivered them into his hands.
33 And he defeated them from Aroer as far as Minnith-twenty cities-and to Abel Keramim, with a very great slaughter. Thus the people of Ammon were subdued before the children of Israel.
Jg 11:34 When Jephthah came to his house at Mizpah, there was his daughter, coming out to meet him with timbrels and dancing; and she was his only child. Besides her he had neither son nor daughter.
35 And it came to pass, when he saw her, that he tore his clothes, and said, "Alas, my daughter! You have brought me very low! You are among those who trouble me! For I have given my word to the LORD, and I cannot go back on it."
36 So she said to him, "My father, if you have given your word to the LORD, do to me according to what has gone out of your mouth, because the LORD has avenged you of your enemies, the people of Ammon."
No, Jephthah did not offer his daughter as a human sacrifice. Notice his vow very carefully in verse 31. He did not intend to commit a human sacrifice:
"then it will be that whatever comes out of the doors of my house to meet me, when I return in peace from the people of Ammon, shall surely be the LORD'S, and I will offer it up as a burnt offering."
Jepthah was referring to an animal sacrifice ("whatever" and "it"). However, he fulfilled the essence of his vow by giving up his daugther to be a perpetual virgin for life. Fathers at this time had authority over their own daughters whether they would marry or not. She would be dedicated to God to serve Him as a single woman for life.
Verses 38 and 39 make this very clear:
Jg 11:38 So he said, "Go." And he sent her away for two months; and she went with her friends, and bewailed her virginity on the mountains.
39 And it was so at the end of two months that she returned to her father, and he carried out his vow with her which he had vowed. She knew no man. And it became a custom in Israel
