The yellowish fluid "colostrum" secreted by mammary glands of mother during the initial days of lactation has abundant antibodies $\left(\mathrm{IgA}\right)$ to protect the infant. This type of immunity is called as:

Immunity is said to be passive when antibodies produced in other organisms are injected into a person to counteract antigens such as snake venom. 

The yellowish fluid ‘colostrum’ secreted by the mother during the initial days of lactation is a form of natural passive immunity. It has plenty of antibodies ($\mathrm{IgA}$) to protect the infant during the initial months of life. Maternal antibodies ($\mathrm{IgG}$) are also transmitted through the placenta. Such an immunity is called natural passive immunity.