The reader of music theory will occasionally see little strings of notes associated with other pitches. These pitch notations will be smaller in size and will sometimes have slashes through them. They are called 'grace notes.' Their function is to add a bit of flavor or expressiveness to the piece. How to interpret and perform these notes varies from composer/performer to composer/performer. Some composers may want the notes played quickly shortly before the notes they precede on the chart. Others will want them played at the same time. So there is some variation in these notes are to be understood, interpreted and performed (Blatter, 12).
Blatter, Alfred (2007). Revisiting Musical Theory. Routledge, Taylor and Francis Group, NY.