I've previously been taught that triglycerides are macromolecules. However, a current professor of mine gave the definition of macromolecules as "polymers of covalently linked monomers". Since, triglycerides aren't formed from repeating monomers, are they considered macromolecules?
Depending on who you ask you will receive a different concept to define macromolecules. These concepts typically arise from the sub-field of those who made the definition, so a polymer chemist is more inclined to consider repeating monomers of exactly one type since that is what plastics are. At the same time, the branch of macromolecular chemistry usually deals with systems that are much smaller than your average multi-domain protein.
The definition most can agree on (to a certain extent) is that macromolecules must be ‘larger’ than ‘small molecules’ (note the pairs of inverted commas). In this definition, it is perfectly reasonable for lipids to be grouped as macromolecules as they are much larger than most secondary metabolites. However, it is true that they are not made up of subunits linearly connected (whether repeating or not) so one may not consider them biopolymers.