What does it mean by "$\chi$ is trivial"?

Question

The following is taken from "A Graduate course in Algebra 1" by Moskowitz and Farmakis

$\color{Green}{Background:}$

$\textbf{Proposition:}$ For an arbitrary short exact sequence of groups

$$A\xrightarrow{\phi}B\xrightarrow{\chi}C\xrightarrow{\psi}D$$

the following are equivalent:

1. $\phi$ is surjective.

2. $\chi$ is trivial.

3. $\psi$ is injective.

$\color{Red}{Questions:}$

For the proposition 2. above, what does $\chi$ is trivial mean?

The use of the term "trivial" is confusing due to that i am not sure if the authors meant that the group is a trivial group being the identity element or they meant something else.

Thank you in advance.