Slurs are markings in music which indicate that successive notes are to be sung or played with only the first note being articulated. This is common in singing where two or more notes may occur while singing a single syllable.
In the following example, the syllable ah is sung on two consecutive notes, and is articulated on each note. Ah is then sung again, covering the same two notes but only articulated on the first note. The curved line joining the two notes indicates a slur.
In the third bar, ah is sung again but this time covering three different notes. Once again the syllable is only articulated on the first note. When singing, slurs can be thought of as "sliding" or "gliding" between notes.
A good example of the way this occurs in a song is the opening phrase of Silent Night which you learned in the previous lesson. It is shown in the following exercise with slur markings.
To keep the music looking as simple as possible, slur markings are often left out of sheet music. You can usually tell where slurs occur because there will be more than one note for a syllable with a small horizontal line written between the lyrics (e.g., Si - lent night).