Vascular plants (tracheophytes) are plants that have complex permanent tissues involved in conducting water, minerals, and food in various parts of the plant. The phloem is the vascular tissue that conducts food materials while the xylem is the one that conducts water and minerals from the roots upwards to the shoot and leaves. Some vascular plants are capable of secondary growth, i.e. a growth characterized by an increase in girth or thickness (as opposed to the primary growth, which is an increase in length). These plants increase in girth or thickness by producing secondary xylem (wood) from the vascular cambium. The wood is produced by woody plants. In this case, the wood that is produced by gymnosperms is referred to as softwood. In contrast, the wood from angiosperms is called hardwood.
Softwood does not necessarily indicate softness. There are softwoods that are harder than some hardwoods. For instance, yews and longleaf pine are much harder than several hardwoods. Some of them are even more resistant to insect attack as some insects prefer hardwood than softwood.