Definition:
Genetic engineering is a technique of directly manipulating an organism's DNA by adding, removing, or modifying specific genes to obtain desired traits. It uses tools such as recombinant DNA technology, gene cloning, and CRISPR.
Applications in Health:
\begin{enumerate}
\item Production of Human Insulin: Using recombinant DNA technology, insulin-producing genes are introduced into bacteria (e.g., E. coli) to produce human insulin for diabetic patients.
\item Gene Therapy: Defective genes causing diseases (e.g., Severe Combined Immunodeficiency - SCID) are replaced or corrected by introducing healthy functional genes.
\end{enumerate}
Final Answer:
\[
\boxed{\text{Genetic engineering is direct manipulation of genes, with health applications such as insulin production and gene therapy.}}
\]