In case of liquids, what does the term streamline refer to? Hiw does it differ from a tube of flow?

LAMINAR (STREAMLINE) FLOW
The flow separates into "layers" that slide relative to one
another without mixing. If we introduce a coloured stream into
the laminar flow, the colour will stay in the stream. The flow is
called steady.
Laminar flow can be represented by a set of lines known as
streamlines (flow lines).
? An individual particle will follow a streamline.
? The flow pattern does not change with time. All particles
starting on a streamline will continue to move on that
streamline.
? A set of streamlines is called a flow tube.
? Streamlines can't cross nor intersect the "walls" of the
flow tube.
? The instantaneous velocity of the particle is in the
direction of the tangent to the streamline.
? Density of streamlines proportional to the velocity:
streamlines close together ? high velocity, streamline far
apart ? low velocity.
? For an ideal fluid, no kinetic energy of the particles is