is triglyceride a polymer?

No.

Polymer: Any of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units, each a relatively light and simple molecule.

Triglyceride: A naturally occurring ester of three fatty acids and glycerol that is the chief constituent of fats and oils.

So, a triglyceride can't be a polymer because it's a fatty compound which only have three units of a fatty acid.

No

lipids which triglycerides are are not polymers because they do not bond the same way they are hydrophobic and have ester linkages not covalent bonds

proteins, carbohydrates all bond the same via covalent bonds using hydrolysis (adds monomers) and dihydration (removes monomers)

Nucleic acids like DNA use a combination of covalent and phosphodiester bonds and are also considered polymers