Masala vs Garam Masala
Masala generally means seasonings of any sort. It is an Arabic origin word in South Asian languages meaning originally in Arabic "a thing which is good and right" (maslahah). Dry masala means spices, ground or whole. Wet masala means a combo of spices plus wet ingredients like tomatoes, onion, garlic, ginger, chiles, etc. and these can be raw and blended, or cooked down in yoghurt and/or tomatoes. They can serve as something that will only be a marinade or that will end up as a gravy, or they can be a garnish. Green masala is cilantro and chopped green chiles as garnish, etc. They can be dry spices cooked in the dish, or added to the dish at the end of the cooking or even at the table. So it is basically the seasoning of the food. The chaat masala is a blend use in the genre of food called chaat. You could call your combo of spices and seasonings the masala for any particular dish, and ask "What masalas do you use in _______" ? fill in the blank with name of dish.
Garam masala is a type of masala, or seasoning. This spice combo is one of the main seasonings used in Pakistani and North Indian cooking as well as other nearby countries like Nepal and Bangladesh. I am not sure if South Indian or Sri Lankan cuisines use garam masala blends so much. But definately every household in the afore mentioned places has a small jar of regulalry freshly ground garam masala blend which is used daily in home cooking.
Garam masala refers to a mix of spices in which the spices give heat to the body according to Ayurvedic principles. Garam means hot. The "garam" spices are like black pepper, cumin, cloves, bay leafs, nutmeg, mace, cardamom big and small, cinnamon, and so forth. Garam masala blends vary from region to region and even home to hom in terms of how much of each "body warming" spice goes in them and in what quantity or ratio of each spice, and some people use a different one for meats versus veg. But whatever the blend, the heat giving properties of the combo make it 'garam.' Garam masala is like an all purpose spice mix used in small quantities in a variety of dishes.
Masala is a fragrant spice blend. It can be either wet (a paste) or dry (a blend of dried, often toasted and ground spices). The pastes frequently include fresh ingredients like cilantro, mint, ginger and garlic along with dried spices and oil. Dishes made with such pastes sometimes have masala in their name (e.g. chicken tikka masala).
Garam masala is a popular dry spice blend. There are many variations, from region to region and cook to cook. Clove, cinnamon, nutmeg/mace and cardamom are fairly common denominators, with several other spices -- including cumin, coriander, pepper and nigella -- often joining the party. Tandoori masala, chatt masala and even panch phoron, the Bengali five-spice blend, are three other members of the large family of dry masalas.