While in GLSL 100, varyings are often defined in both the vertex and fragment shaders, the varying qualifier has been removed in GLSL 300 ES. That is, varying qualifiers are updated with their appropriate in and out qualifiers, depending on whether the values are provided as inputs or returned as outputs. For example, consider the following from GLSL 100:

// inside of the vertex shader
varying vec2 vTexcoord;
varying vec3 vNormal;

// inside of the fragment shader
varying vec2 vTexcoord;
varying vec3 vNormal;

This would be changed to the following in GLSL 300 ES:

// inside of the vertex shader
out vec2 vTexcoord;
out vec3 vNormal;

// inside of the fragment shader
in vec2 vTexcoord;
in vec3 vNormal;