A budget line represents the different combinations of two goods that are affordable and are available to a consumer; while being aware of his/her income-level and market prices of both the goods.
\\(\\begin{array}{l}{\ ext { Let } x_{1} \ ext { be the amount of good } 1 \ ext { . }} \\\\ {x_{2} \ ext { be the amount of good } 2 \ ext { . }} \\\\ {P_{1} \ ext { be the price of good } 1} \\\\ {P_{2} \ ext { be the price of good } 2 \ ext { . }}\\end{array}\\)
\\(\\begin{array}{l}{\\mathrm{P}_{1} \\mathrm{x}_{1}=\ ext { Total money spent on good } 1} \\\\ {\\mathrm{P}_{1} \\mathrm{x}_{2}=\ ext { Total money spent on good } 2} \\\\ {\ ext { Then, the budget line will be: }} \\\\ {\\mathrm{P}_{1} \\mathrm{x}_{1}+\\mathrm{P}_{2} \\mathrm{x}_{2}=\\mathrm{M}}\\end{array}\\)
All the consumption bundles on the budget line cost the consumer exactly the equivalent of hi/her income.