what do you mean by weak entity set
Weak entity In a relational database, a weak entity is an entity that cannot be uniquely identified by its attributes alone; therefore, it must use a foreign key in conjunction with its attributes to create a primary key. The foreign key is typically a primary key of an entity it is related to.
Denial-of-service attack A wide array of programs are used to launch DoS-attacks.
Hermitian matrix The diagonal elements must be real, as they must be their own complex conjugate.
Strait Straits are the converse of isthmuses. That is, while a strait lies between two land masses and connects two larger bodies of water, an isthmus lies between two bodies of water and connects two larger land masses.