Pose is a FlexMotionLayer state where the motion is fixed at a given time.

There is clear distinction between pause and pose, though. The former actually impacts every motion layer of a given mask layer and, thus, their transitions. The latter only impacts that one motion layer and doesn't prevent in and out transitions from occurring.

There are multiple ways to set a pose:

using SV.FlexMotion;
using UnityEngine;

public class PoseFlexMotionLayer : MonoBehaviour
{
    [SerializeField]
    private FlexMotionAnimator animator;
    
    [SerializeField]
    private AnimationClip clip;

    private FlexMotionLayer _layer;

    private void Start()
    {
        // Apply a pose through method chaining
        // This will pose the animation at a "50%" time. 
        _layer = animator.Play(clip).SetPose(0.5f);
        
        // Stop or start a pose through the dedicated switch method.
        _layer.SwitchPose();

        // The same but using the dedicated property.
        _layer.IsInPose = true;
        
        // Which can be followed (or preceded) by applying a desired time
        // using one of the time-related methods and properties.
        _layer.NormalizedTime = 0.25f;
    }
}

And, obviously, a newly played animation will not be posed (unless specifically set as such) and the transition will happen as expected.