Final answer:
Telegraphic speech is where critical content words are used while omitting "frill" words, similar to messages sent via telegraph to be concise.
Step-by-step explanation:
The speech characterized by two- to three-word sentences that contain critical content words but omit "frill" words is known as telegraphic speech.
This type of speech is commonly seen in the early language development of children, where they include essential words to convey a message, but leave out less critical elements such as articles, prepositions, and auxiliary verbs.
This streamlined form of communication is named after the concise nature of messages sent via telegraph, where unnecessary words were omitted to save time and cost.