When the Jews speak of the Son of David, they are referring to Christ. 2 Sam 7:12-14, Ps 132:11, Isa 11:1-2, Jer 23:5, Mt 21:9-11, Ps 118:26

The Old Testament prophesied that Christ would come as a descendant of David. (2 Sam 7:12-14, Ps 132:11, Isa 11:1-2, Jer 23:5)

2 Sam 7:12 And when thy days be fulfilled, and thou shalt sleep with thy fathers, I will set up thy seed after thee, which shall proceed out of thy bowels, and I will establish his kingdom. 13 He shall build an house for my name, and I will stablish the throne of his kingdom for ever. 14 I will be his father, and he shall be my son. If he commit iniquity, I will chasten him with the rod of men, and with the stripes of the children of men:

Ps 132:11 The Lord hath sworn in truth unto David; he will not turn from it; Of the fruit of thy body will I set upon thy throne.

Isa 11:1 And there shall come forth a rod out of the stem of Jesse, and a Branch shall grow out of his roots: 2 And the spirit of the Lord shall rest upon him, the spirit of wisdom and understanding, the spirit of counsel and might, the spirit of knowledge and of the fear of the Lord;

Jer 23:5 Behold, the days come, saith the Lord, that I will raise unto David a righteous Branch, and a King shall reign and prosper, and shall execute judgment and justice in the earth.

Jesus is the son of David, the Christ. (Mt 12:22-23, Mt 21:9-11, Ps 118:26)

Mt 12:22 Then was brought unto him one possessed with a devil, blind, and dumb: and he healed him, insomuch that the blind and dumb both spake and saw. 23 And all the people were amazed, and said, Is not this the son of David?

Mt 21:9 And the multitudes that went before, and that followed, cried, saying, Hosanna to the son of David: Blessed is he that cometh in the name of the Lord; Hosanna in the highest. 10 And when he was come into Jerusalem, all the city was moved, saying, Who is this? 11 And the multitude said, This is Jesus the prophet of Nazareth of Galilee.

Ps 118:26 Blessed be he that cometh in the name of the Lord: we have blessed you out of the house of the Lord.