Definition of Anode:
An electron collector. Means up the path from a negative to a positive voltage. An anode has a more positive voltage relative to a cathode.
An anode is an electrode through which electric current flows into a polarized electrical device. The direction of electric current is, by convention, opposite to the direction of electron flow. In other words, the electrons flow from the anode into, for example, an electrical circuit. Mnemonic: ACID (Anode Current Into Device).
A widespread misconception is that anode polarity is always positive (+). This is often incorrectly inferred from the correct fact that in all electro-chemical devices, negatively charged anions move towards the anode (hence their name) and positively charged cations move away from it. In fact anode polarity depends on the device type, and sometimes even in which mode it operates, as per the above electric current direction-based universal definition. Consequently, as can be seen from the following examples, the anode is positive in a device that consumes power, and the anode is negative in a device that provides power:
In a discharging battery or galvanic cell (diagram at below), the anode is the negative terminal because it is where the current flows into “the device” (i.e. the battery cell). This inward current is carried externally by electrons moving outwards, negative charge moving one way constituting positive current flowing the other way.
In a recharging battery, or an electrolytic cell, the anode is the positive terminal, which receives current from an external generator. The current through a recharging battery is opposite to the direction of current during discharge; in other words, the electrode which was the cathode during battery discharge becomes the anode while the battery is recharging.
In a diode, it is the positive terminal at the tail of the arrow symbol (base of the triangle), where current flows into the device. Note electrode naming for diodes is always based on the direction of the forward current (that of the arrow, in which the current flows “most easily”), even for types such as Zener diodes or solar cells where the current of interest is the reverse current.
Explanation with Diagram: