Grub has two common meanings that come from very different origins:

1. Food, especially simple or hearty food. When someone says “let's grab some grub,” they mean let's get something to eat. The word has a casual, down-to-earth feeling. Cowboys on the trail ate grub cooked over campfires, and the person who prepared their meals was sometimes called the grub cook. Today, you might hear someone say the cafeteria serves decent grub, or ask what kind of grub you're having for dinner.
2. A soft, wormlike larva of an insect, especially a beetle. Garden grubs live in soil and eat plant roots. They look pale and squishy, with tiny legs near the front of their bodies. Birds love eating grubs, and if you've ever seen a robin pulling something fat and whitish from the ground, it was probably a grub. These larvae eventually transform into beetles. Some people around the world actually eat certain types of grubs as food, though that's not what people in the United States usually mean when they talk about grub!