What's the difference between classification and regression?

Both are supervised learning. Classification predicts a discrete category (spam/not-spam, which digit); regression predicts a continuous number (price, temperature). The distinction drives your choice of model output, loss function (e.g. cross-entropy vs mean-squared-error), and metrics (accuracy/F1 vs RMSE/MAE). Some problems can be framed either way — predicting an exact age (regression) vs an age bracket (classification).