Word problems involve translating the English statement of a problem into mathematical notation, then solving it using mathematical manipulation. For most students, the hardest part is in that first step -- translation from English to math-ese. If it is done right, then the rest is easy.
Techniques common in word problems are translating from English to mathematical notation, working with percentages, solving distance = rate * time problems, working with compound interest, and "work" problems, to name a few.
In Calculus, students will find "related rates" problems. In some Calculus texts, linear programming is also addressed, so students often get the joy of these problems together with the Calculus bliss they already signed up for.