The term vocabulary refers to the words that we understand and can use in communication. Research identifies four different types of vocabulary: listening, speaking, reading, and writing. Each type references the words we know or can use across these four different domains of communication. Vocabulary knowledge plays a critical role in reading comprehension, as students must be prepared to either understand the words they read or use a strategy to fill-in gaps in meaning.
Students gain the majority of their vocabulary knowledge indirectly - through exposure to a rich variety of words, from frequent and consistent experiences with reading. Readers also require some direct skill instruction; specifically, students should be modeled and taught strategies for determining the meanings of unfamiliar words while reading. Ch. 4 of Put Reading First also points out that "direct instruction helps students learn ... words that represent complex concepts that are not part of the students' everyday experiences." (30) Therefore, teachers should include some direct word instruction in their curriculum to address these conceptual or niche terms that students will not likely encounter elsewhere.
The "Marzano Method" is one popular strategy for direct vocabulary instruction. Check out the following video for more details and examples of the Marzano Method at work: