Tack refers to the amount of pull resistance or stickiness exhibited by an adhesive when attempting to separate two substrates while the adhesive is still in a viscous or fluid state. This property is crucial in determining the initial bonding strength of the adhesive, ensuring that materials remain in place until the adhesive fully cures. Tack is also a relevant property in inks, indicating their ability to adhere to surfaces upon application. High tack ensures immediate adhesion, which is important in various applications such as labeling, packaging, and printing.