What is the meaning of besieged in hobbit?

In the context of J.R. R. Tolkien's fictional universe of Middle-earth, the word "besieged" is used to describe the situation of the characters in the novel "The Hobbit". The protagonist, Bilbo Baggins, and his companions, are trapped in the Lonely Mountain by the dragon Smaug, who is guarding a vast treasure. The dragon has been angered by the dwarves, who have been trying to reclaim their lost kingdom of Erebor. Bilbo and the dwarves are essentially under siege, as Smaug is preventing them from leaving the mountain and claiming the treasure.