Interlard refers to speech or writing and it means "to load up with" or "to pepper." Your mom's request that you come to a family dinner might be interlarded with references to how often lately you've been out with friends.
Are you wondering about seeing lard inside interlard? In the 15th century, interlard came into English from Middle French, where it meant to "mix with alternate layers of fat." Yum, right? :-) Maybe not, but important to remember, as interlarded speech or writing is well-greased in a figurative way. Think of your math teacher's lessons interlarded with jokes from The Simpsons :-) or a word-learning blurb interlarded with smiles :-).