A plug connector and a mating plug connector for connecting lines for liquid or gaseous media, the plug connector comprising - a connector body, which has at least a first casing section, which forms a receiving space for receiving a part of the mating plug connector, wherein at least two passages are formed in the first casing section; - a locking element, which is provided for securing the plug connector relative to the mating plug connector, wherein the passages in the first casing section of the connector body serve to receive the locking element, wherein an indicator element is formed, and wherein a guide receptacle for receiving the indicator element in a displaceable manner is formed, wherein the indicator element is received in the guide receptacle such that the indicator element is displaceable between a rest position and an indicator position, wherein the indicator element has an indicator surface, which is visible in the indicator position of the indicator element and, in the rest position of the indicator element, is at least partially concealed, characterized in that the indicator surface, when it is visible, serves to signal that the plug connector is plugged into the mating plug connector correctly, and that the locking element is locked correctly, wherein the guide receptacle is designed in the form of a guide sleeve, which is coupled to the holding region of the locking element, wherein the indicator element, in its rest position, is arranged within the guide receptacle and, in its indicator position, at least partially protrudes relative to the guide receptacle, wherein the indicator element is coupled to an actuation region, which is greater than a groove width of a securing groove of the mating plug connector, wherein the actuation region is designed such that it abuts in an outer region of the securing groove, so that it urges the indicator element into the indicator position when all latching regions of the locking element engage with the securing groove of the mating plug connector. - a connector body, which has at least a first casing section, which forms a receiving space for receiving a part of the mating plug connector, wherein at least two passages are formed in the first casing section; - a locking element, which is provided for securing the plug connector relative to the mating plug connector, wherein the passages in the first casing section of the connector body serve to receive the locking element, wherein an indicator element is formed, and wherein a guide receptacle for receiving the indicator element in a displaceable manner is formed, wherein the indicator element is received in the guide receptacle such that the indicator element is displaceable between a rest position and an indicator position, wherein the indicator element has an indicator surface, which is visible in the indicator position of the indicator element and, in the rest position of the indicator element, is at least partially concealed, characterized in that the indicator surface, when it is visible, serves to signal that the plug connector is plugged into the mating plug connector correctly, and that the locking element is locked correctly, wherein the guide receptacle is designed in the form of a guide sleeve, which is coupled to the holding region of the locking element, wherein the indicator element, in its rest position, is arranged within the guide receptacle and, in its indicator position, at least partially protrudes relative to the guide receptacle, wherein the indicator element is coupled to an actuation region, which is greater than a groove width of a securing groove of the mating plug connector, wherein the actuation region is designed such that it abuts in an outer region of the securing groove, so that it urges the indicator element into the indicator position when all latching regions of the locking element engage with the securing groove of the mating plug connector.