Indifference curves and budget constraints

Customer indifferene curve
Convex curves that do not intersect and are based on assumptions that:

• More is preferable to less
• Goods are substitutable.
• Marginal utility of a good falls as more of it is consumed.
• Infinite no. of indifference curve.
• The higher the indifference curve, the greater the utility
  

Budget constraint (for money economy)
Straight line that defines combinations of the goods that an individual can afford. Point of tangency between budget constraint and highest obtainable indifference curve is optimal level of consumer satisfaction. ( consumption opportunity constraint for barter economy)

Increase in income shifts the budget constraint line to right, while the substitution effect rotates the budget constraint line.