Think of a combination reaction like two Lego bricks snapping together to make one bigger piece, whereas combustion is like burning wood where fuel breaks down and reacts with oxygen to release heat, light, and gases.

COMBination = COMBine multiple reactants into ONE product ($A + B \rightarrow AB$).

In a combination reaction (also known as synthesis reaction), the general form is $A + B \rightarrow AB$. For example, calcium oxide reacts with water to form slaked lime ($CaO + H_2O \rightarrow Ca(OH)_2$), and hydrogen reacts with oxygen to form water ($2H_2 + O_2 \rightarrow 2H_2O$). Conversely, the burning of natural gas ($CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$) and the decomposition of silver chloride ($2AgCl \xrightarrow{sunlight} 2Ag + Cl_2$) belong to combustion and decomposition reaction categories, respectively.