My translation:

In some cases, one needs to express semi-major axis and eccentricity of an elliptic orbit through parameters (speed and radius) of the circular orbit passing through a certain point of the elliptic orbit (Fig 1.3). Let's represent the spacecraft's velocity as a sum

$V = V_{circ} + \Delta V$,

where $V_{circ}$ is the velocity of movement along the circular orbit of radius $r$, determined by formula (1.4);

$\Delta V$ is the velocity relative to the circular, required to attain the actual velocity.

So, as the text says, for a given point of a given elliptic orbit, $V_{circ}$ or $V_{кр}$ is the velocity that a circular orbit that passes through this point (and lies in the same plane as the elliptic orbit, presumably) has at this point. And $\Delta V$ is the difference between $V$, which is the velocity of the elliptic orbit at this point, and $V_{circ}$.

It's probably explained later in the book what they need to represent $V$ as such a sum for.

My translation:

In some cases, one needs to express semi-major axis and eccentricity of an elliptic orbit in terms of parameters (speed and radius) of the circular orbit passing through a certain point of the elliptic orbit (Fig 1.3). Let's represent the spacecraft's velocity as a sum

$V = V_{circ} + \Delta V$,

where $V_{circ}$ is the velocity of movement along the circular orbit of radius $r$, determined by formula (1.4);

$\Delta V$ is the velocity relative to the circular, required to attain the actual velocity.

So, as the text says, for a given point of a given elliptic orbit, $V_{circ}$ or $V_{кр}$ is the velocity that a circular orbit that passes through this point (and lies in the same plane as the elliptic orbit, presumably) has at this point. And $\Delta V$ is the difference between $V$, which is the velocity of the elliptic orbit at this point, and $V_{circ}$.

It's probably explained later in the book what they need to represent $V$ as such a sum for.