Iron-deficiency anemia can cause fatigue (tiredness), shortness of breath, chest pain, and other symptoms. Severe iron-deficiency anemia can lead to heart problems, infections, problems with growth and development in children, and other complications.
Semantics is the study of meaning. It is a wide subject within the general study of language. An understanding of semantics is essential to the study of language acquisition (how language users acquire a sense of meaning, as speakers and writers, listeners and readers) and of language change (how meanings alter over time).
In theoretical linguistics, semantics is the study of meaning in language. One way to view meaning is as the connection between language and world. For instance, consider the sentence It's raining in Boston. What is the world like when this sentence is true?